Bolting Guidance and Information

General Information and Guidance on Bolting

by Francis Haden

Bolt Type

Bolts used by rock climbers exist in two types; expansion bolts and glue-in, or as more commonly known; resin bolts.

Broadly, a climb can be equipped faster using expansion bolts and they require less equipment to install. Resin bolts do require additional items of equipment, cannot be loaded immediately however once placed, this type of bolt lasts longer and has many more advantages.

Expansion Bolts

A mechanical fixing that works by expanding and compressing against the wall of the hole drilled into the rock. The typical climbing expansion bolt features a hanger attached to the expansion bolt and secured by way of a nut and washer. Some expansion bolts have a continuous sleeve, rather than just a shorter sleeve towards the end of the bolt. Other varieties have double wedge and sleeve features however in all cases the overriding principle remains the same

An exception to the above is the Long Life expansion bolt produced by Petzl. This complete unit achieves the expansion effect by hammering a centrally located pin to produce the wedging effect.

Other varieties of expansion bolt that maybe found on rock climbs but are generally meant for caving, consist of a self driving anchor into which a hanger is screwed after the sleeve has been drilled sufficiently deep. The threaded sleeve has teeth cut at one end, is screwed onto a handled driver then hit and rotated to ‘self drill’ the bolt hole. A spreader cone of metal is placed in the rear of the anchor and the assembly hit back into the hole causing an expansion cone to form. The hanger is generally made of aluminium (this system was developed for expedition caving) therefore not expected to be left permanently attached due to issues of dissimilar metal corrosion with the anchor that is made of steel.

A 10mm version designed for climbing was produced by Petzl, driven using an adaptor fitted to the hand driver. Due to the significant time in hand drilling a single placement these never proved popular.


Expansion bolts are installed by drilling a hole at right angles to the rock face, removing any dust using a piece of flexible tube or a hand pump then hammering the assembly into the bolt hole. The nut is kept just below the end of the bolt to prevent the threads being damaged by hammer blows. The hanger is aligned in the direction of any load and the nut tightened thereby driving the sliding sleeve over the wedge shape end of the bolt.

Battery powered drilling of typical expansion bolts and Petzl Long Life bolt

Hand drilling 8mm caving use expansion bolts (same for the climbing 10mm version)

Battery powered drilling of the above bolt types


  • Minimal amount of equipment required to install (drill, hammer and spanner)
  • A load can be applied immediately
  • Easy to place on severely over hanging rock.


  • Hangers often work loose making clipping awkward or become lost as a result
  • Hangers cause karabiner damage due to the sharp edges
  • Hangers can be stolen
  • Not easily replaced using the same sized hole if rendered unusable by corrosion
  • Continually stress the rock – this can accelerate corrosion due stresses exerted into the metal
  • Expansion bolt within the rock is not protected (see resin bolts)
  • Hanger and bolt metal grades must be matched to prevent accelerated corrosion due to dissimilar metals
  • Cannot be retreated from without leaving a karabiner or quick link
  • Dangerously unsuitable if installed in certain rock types (soft sandstone)

Resin (Glue-in) Bolts

Resin bolts are secured by the adhesion of a suitable resin with the rock surface inside the hole and a mechanical keying effect where the resin contacts the bolt. A popular misconception is that the resin sticks to the bolt and that provides the holding power. In reality the holding power between resin and metal is achieved by grooves stamped into the bolt or by twists in the metal. Resin bolts are a single piece unit formed either by a forging process or more commonly through the use of metal bar bent into shape, with or without welding.

Most producers of resin bolts offer longer bolts that can be fixed deeper into the rock to increase the strength of the placement or where poor rock exists as a surface layer and the hole needs to be deeper to gain an acceptable depth of placement.


  • Significantly stronger bolts than a comparable depth expansion bolt
  • Cannot be stolen
  • No parts that can rotate loose
  • No karabiner damage
  • Can be abseiled from by directly threading the rope through the eye
  • Typically have greater corrosion resistance
  • Single piece unit – dissimilar metal corrosion is not an issue
  • Can improve holding power by installing a longer bolt
  • Best overall system for long life
  • The only sustainable fixed protection system (titanium resin bolts) for SCC affected regions
  • The only type of fixing suitable for all rock types


  • More equipment required (hole cleaning brush, blower, resin gun + drill and hammer)
  • Hole preparation (removal of dust) is crucial to installing a safe bolt
  • The majority of resin bolts do not (Bolt Product excepted) feature a means of retention whilst the resin is hardening if placed upside down (this depends on the resin however – some are fast acting eg glass ampoules)
  • Can be messy using bulk resin dispensing systems depending on how well the user has been trained
  • Resin does have a shelf life
  • Cannot immediately load the bolt. Resin cure times vary from a couple of hours to a day.


As for expansion bolts, the hole for a resin bolt is generally drilled at or slightly off perpendicular to the rock surface depending on whether the bolt requires counter sinking into the face. It is generally accepted that resin bolts that use a twist leg design (Bolt Products, DMM Eco Bolt, Wave Bolt) do not require the eye to be recessed (notched) into the rock surface. The opposing metal legs provide a very high resistance to torque loading whereas a single shaft resin bolt is more like to twist. The loads however to achieve sufficient torsion have to be high and in many cases the attachment link eg karabiner, would fail beforehand. The EN 959 and UIAA-123 Rock Anchor test does not require bolts to be recessed.

A blow pump and small brush are used in conjunction for the removal of loose dust and to clean the inside of the hole.

The resin either comes in the form of single use glass ampoules or a bulk dispensing system (eg Hilti, Ramset, Sika, Exchem).

Glass ampoules are ideal for placing a single bolt and have the added advantage that the resin gels (hardens) very quickly so for inverted placements on steep rock the bolt can be held until the resin has hardened sufficiently to prevent slumping of the bolt. Glass ampoules do not have sufficient resin volume for use with bolts that are expected to be counter sunk. Typically ampoules are used with Petzl Collinox and Petzl Batinox rings.

Bulk dispensing systems are far more common and consist of a dispenser into which a cartridge or collapsible foil pack is loaded. In the case of collapsible foil packs (eg Hilti RE 500 & HY 150) the pack is placed inside a rigid foil pack holder that can be reused. The resin comprises two separate components that are discharged via trigger pulls into a mixer nozzle previously screwed onto the front of the dispenser. A prescribed number of trigger pulls are initially required to ensure sufficient mixing and this resin is typically discarded into the plastic packaging. A color change is typically associated with this process and an extension tube for deep holes may also be attached to the tip of the nozzle.

The mixer nozzle is placed at the back of the hole and retracted slowly as the resin is injected; the tip of the nozzle must be kept inside the resin to ensure air pockets are not trapped inside the hole. The bolt is then rotated as it is pushed into the resin to work the resin over the shaft of the bolt. As the bolt is pushed into the resin, any excess discharged is used to fill any gaps around the eye of the bolt. This process can be messy unless surgical gloves and rags are used to wipe away excess resin. Most dispensers also require the catch located on the rear to be depressed to alleviate the pressure on the pack and stop resin dribbling from the nozzle when not in use.

Resin type can vary significantly in appearance, permeability, dispensing method, reaction times and strength once fully cured. Of the various resin types, hybrid urethane / methyacrylate (Hilti HY 150), hybrid / epoxy urethane (Hilti RE 500) and glass ampoules containing vinyl ester (Fischer / Upat / Fixe) are of predominant use by climbers.

All resin systems feature a gelling time and a curing time, both times are affected by the base material temperature. The gel time is the shorter time in which the resin remains viscous i.e free flowing. The cure time specifies when the bolt can be fully loaded and for climbers is particularly important in ensuring that the bolts are not used beforehand.

Equipping New Routes

The conception of a new route is often from the obvious gap in-between existing climbs or the development of an entirely new climbing area. Quality routes link obvious natural rock features on sound rock and preserve the character and independence of neighboring climbs. Adding a new climb that shares holds or crosses over existing routes not only leaves a contrived experience but can cause problems for other climbers climbing the other route (s).

Once the line is chosen, an abseil inspection is the next stage to confirm the rock is suitably sound for climbing upon and installing safe bolts. The choice of bolt type will take into account the environment, number of bolts to install and rock type. Fatal accidents have been caused (eg Blue Mountains, Australia) by the installation of unsuitable bolts for the rock properties.

Prior to bolting the line will be cleaned of loose rock and vegetation from the top down to progressively clean off any dirt that has fallen onto handholds / ledges below. Once cleaned, the bolt locations need to be determined and their positions marked for drilling.


  • Bolts are closer spaced nearer the ground to minimize the likelihood of ground falls
  • May be spaced further apart higher up
  • Cruxes typically feature a bolt to protect the harder moves and allow the climber to aid past onto easier ground if the climb proves too difficult.
  • Placements need to sync with the rhythm of climbing
  • Be placed next to a solid hold to clip from
  • Can be clipped by shorter climbers
  • Allow the rope to run with the minimum  of friction
  • Pull the rope away from sharp edges
  • Be placed so as not to obscure holds once the rope has been clipped into a quick draw

Crucially the route should be bolted for the grade and not in reflection of the person equipping the line. Ethics aside, sport climbing is considered a well protected style of climbing and bolting routes with long run outs or protection far from cruxes is contrary to what this style of climbing is supposed to offer.

Depending on the individuals’ experience and how involved it is to equip the line (eg multi pitch) will determine whether a top rope / self belay is required to ensure the bolts are appropriately placed.

Belays and lower offs are located to enable an easy recovery of quick draws but allows the rope to hang to the side of a climber when top roping. A minimum of 2 bolts must be used and spaced such that the spacing reflects 2 times the depth of the bolt placement. This ensures that in the event of one bolt failing, the other will provide the necessary back up.

For expansion bolts, the route will be drilled and equipped bolt by bolt. For resin bolts it is generally the most economic use of the resin pack to prepare all bolts then glue up the entire route in one go as this minimizes the wastage of glue. Resins packs do not need to be fully used in one time however partly used packs require the initial trigger pulls of resin to be discarded as if it were a new pack. The volume ‘wasted’ is significant in that it will typically glue in several bolts.

Ultimately equipping new routes requires a high degree of organization if the output is to be worthwhile. Equipment is best linked to the harness using cord lanyards to prevent loss and ensure everything is easily accessible.

A new climb being equipped with resin bolts on overhanging limestone. Note the blow pump, hammer attached to lanyards and the use of a rope access sit harness.

Climbers who regularly equip new routes tend to prefer the use of static rope as it is more efficient to ascend upon and less prone to being cut by edges. Single rope technique (SRT) and rigging static lines with re-belays and deviations is proven to be more efficient than other forms of rigging such as self top roping. Consideration must also be given to the prolonged length of time spent hanging on the rope therefore many opt for commercial rigging harnesses that provide the comfort and attachments capable of suspending heavy weights eg drills.

Bolt Life

Many factors affect bolt life, predominantly these are climate and the bolt type. With the development of bolt systems and decrease in relative costs, sport climbing areas are typically equipped using stainless steel bolts rather than plated bolts and hangers.

With significant failures of expansion bolts in coastal limestone sport climbing regions (Thailand, Cayman Islands, Malta) a greater awareness of the benefits from using resin bolts have seen an increase in the use of this type of fixing.

Awareness of local conditions and knowledge is critical in ensuring the appropriate specification of bolt is used for routes to be equipped safely.

Metal Types & Grade

Expansion bolts are produced in galvanized steel and stainless steel, the common variety being stainless steel at A2 or AISI 304 grade as this generally represents the a good balance between cost and corrosion resistance. For environments where corrosion is an issue; eg marine environments, a marine grade stainless steel is used and this is designated A4 or AISI 316. Resin bolts have a distinct advantage compared to expansion bolts as they can be manufactured in standard steel, marine grade stainless steel and critically titanium.


The rate of oxidation (rusting) of the metal typically determines the lifespan of a bolt and when saltwater is present in the atmosphere this accelerates the corrosion process and marine grade steel is a mandatory requirement.

Even in non-marine environments, matching the grade of all metal used is critical in preventing another form of corrosion; dissimilar metal corrosion. The electrochemical difference in metal type creates a sacrificial process where metal ions move from the more anodic metal to the more cathodic metal.
The image to the right provides an example of dissimilar metal corrosion caused by the combination of aluminium hangers and normal steel chain.

Rock type and proximity to the sea can rapidly accelerate corrosion. The combination of magnesium ions in limestone reacting with chlorine ions in saltwater to form magnesium chloride has rendered marine grade bolts in Thailand and the Cayman Islands unsafe in a year. The surface appearance would suggest the bolt is safe to use however body weight in most cases is sufficient to break the bolt. This is known as Stress Corrosion Cracking (SCC) and is the result of a combination of three factors – a susceptible material (stainless steel), exposure to a corrosive environment (chlorides in this case) and tensile stresses above a threshold (expansion bolts).

In South Thailand, where SCC is a serious issue, Petzl Collinox marine grade resin bolts formed by hot forging have resisted SCC no doubt in part to the absence of material cracks.

Ultimately the only solution in those areas is to switch bolt and metal type to a titanium resin bolt in combination with an epoxy resin.


Resin bolts typically last longer than a comparable expansion bolt because the majority of the metal is protected by resin (no air gap) and no stress is present until the bolt is loaded by a climber. The hanger on an expansion bolt rarely sits perfectly flat and the complex loading exerted through the metal hanger from the expansion bolt acts as a catalyst once corrosion has developed in the metal.

Tests conducted by Deutscher Alpine Verien (DAV) on 15 year old resin bolts found no loss in strength and the general consensus seems to be that glued-in bolts have an almost indefinite life span.

Bolt Testing

Testing of bolts is either performed at dedicated testing facilities that load test materials or at climbing areas using purpose built, man portable testers.

There are three failure modes possible; bolt failure, rock failure and a combination of both. Regardless of the load direction, modern bolts fail in tension, the rock crushes and the bolt slides out even when radially loaded.

The EN 959 test requires a fall resistance of 25kN and an extraction resistance of 15kN, the UIAA 123 requirements is 25kN fall and 20kN extraction. This test is performed in a concrete block of 50N/mm2 which in practical terms is a medium to low strength rock type.

The use of auto lock devices in sport climbing can generate very high impact loads on fixed protection and in combination with friction, the requirement for bolts to hold 15kN is not a particularly high target, especially in combination with weaker rock types and variability in the rock itself.

Testing is typically conducted axially (worst case) and under increasing, static load to failure. Since bolts are designed for use with an energy absorbing element; a climbing rope, the load in a fall therefore becomes a force on the bolt. The bolt itself cannot absorb force, it transmits it into the surrounding rock mass.

For testing outdoors, portable testers consist of a hydraulic cylinder mounted on a tripod, linking arm and attachment eye which is linked to the bolt using a high strength steel quick link or karabiner. A hand pump is linked via a length of flexible hose and a pressure gauge used to record the pressure which is converted into kilo Newton.

Pull testing of a Bolt Products stainless steel marine grade 6mm * 80mm resin bolt in granite. The linking karabiner failed at 55kN.

Hong Kong Bolts

Climbing was established in Hong Kong well before the advent of resin bolt technology so expansion bolts are predominantly found in Hong Kong. For inland crags, AISI 304 or A2 sufficiently resists normal levels of corrosion however it is common to find marine grade stainless steel bolts on Lion Rock and other inland venues. The cost difference between the grades of metal for expansion bolts is minor in the context of the better corrosion resistance gained. Typical sizes are 10mm and made by Fixe or Petzl, it is rare to see 12mm versions of these bolts.

Throughout coastal climbing areas such as Tung Lung, marine grade 10mm expansion bolts are found on the majority of routes. Corrosion problems are usually associated with the bolt hanger and any surface exposed metal, such as lower off hardware, rather than the expansion bolt itself. Local knowledge places an approximate 10 year life span on this type of fixing and this was confirmed by recent bolt pull testing on Technical Wall (August 2012).

Fortunately Hong Kong does not have to contend with aggressive SCC given the lack of any limestone in the region however expansion bolts placed around coastal areas remain at risk from non accelerated SCC.

Example of SCC found in an expansion bolt hanger on Technical Wall, Tung Lung. The bolt hanger failed at 5kN, well below the EN 959 test requirement.

Cape Collinson on Hong Kong Island is currently the only area that exclusively uses glue in bolts however other climbing areas throughout Hong Kong are seeing an increasing number of resin bolts installed. To resist long term corrosion and minimize the reasonably regular replacement of hangers (and bolts) that ultimately drive costs upwards, a gradual policy of replacing expansion bolts with high grade 316 stainless steel bolts offers the best long-term solution.

Since Hong Kong is a sport climbing region, the challenge facing the local climbing community is the awareness of the need to maintain in-situ protection via a community based approach.

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Perhaps this is a good reason for investing in a trad rack, and avoid bolting lines that can be lead with traditional gear. Of course, placing trad pro has risks. But, at least you avoid the risk associated with difficult to detect SCC. Plus, trad is rad. On a more serious note, I have noticed that some routes have lack chains or rappel rings. Others have chains of questionable strength (look like they just came from the local hardware store). One route I came across – Angel’s Wing, Beacon Hill – had chains to a single mallion for lowering. It… Read more »