|This article does not cite any references or sources. (September 2012)|
A climbing hold is a shaped grip that is usually attached to a climbing wall so climbers can grab or step on it. On most walls, climbing holds are arranged in paths, called routes, by specially trained route setters. Climbing holds come in a large array of sizes and shapes to provide different levels of challenge to a climber. Climbing holds are either bolted to a wall via hex-head bolts and existing t-nuts or they are screwed on with several small screws. In extreme cases, concrete anchors may be used (if putting holds on the underside of a bridge, for example).
Early climbing holds were made from real rocks that were cast into concrete blocks, later they were rocks with holes drilled in them so they could be attached to a wall. While the feel of these holds is realistic, rock holds are heavy and can polish with a lot of use. Rock holds are also difficult to manufacture, However a company call Realholds in the uk has setup processing many types of natural stone holds for indoor climbing walls.
Wood was another early hold-making material, mainly because it was inexpensive and easy to carve into various shapes. It is still used today in various forms for homemade and commercially produced handholds. Wood holds are usually smooth and pleasant to grab, though they are difficult to wash and splintering may become a possibility with age. The Schoolroom, a famous private training gym in Sheffield, England has a plethora of challenging homemade wooden holds, and Ben Pritchard's infamous short Splinter features Malcolm Smith using wooden holds to re-create the moves and holds on Hubble (a difficult outdoor problem he was training for). Wolfgang Gullich made the first campus board with wooden rungs to help him train for his 9a route action directe.
In the early days, most companies that manufactured holds used a resin mixture. Well-mixed resin can create fairly durable hold, though as the holds age they become more and more brittle and may eventually crack. The edges of resin holds are prone to chipping, and between holds getting dropped, put into buckets with other holds, tossed around, and washed, resin holds quickly take on a beat up appearance. Furthermore, the chipped or broken edge of a resin hold can often provide an unintended place to grab that can be sharp or otherwise dangerous to the climber. Because resin holds are not flexible, they will often crack suddenly if they are being tightened down on a wall that is not completely flat. A final problem is the weight of resin holds. As hold sizes have grown and grown, in many cases resin has become an impractical material to use. Even when the hold is hollow-backed, resin is still quite a heavy material to be carried up the wall in a bucket.
A company called Realholds from the Peak District in the United Kingdom specializes in cutting, drilling and testing many natural stone types for use in indoor climbing walls. These holds are intended to give climbers a real stone feel. Due to processing costs, they are more expensive than resin holds and require extra care when installing. However, the company claims they are more environmentally friendly and can bring the feeling of outdoor climbing to indoor climbing walls. 
A company called Voo Doo Holds out of Arizona, USA has long used a softer mixture for their holds and included a rubber-like backing on each hold in an effort to prevent the holds from spinning. This technique has had mixed success, as eventually the rubber backing begins to peel away from the wall, providing a similar unintended handhold as the chipped resin might. The softer mixture is more durable than a brittle resin, but with uneven climbing walls and overtightening these holds develop slow cracks that eventually render the hold useless.
Synrock, from the east coast of the United States, has been experimenting with combining synthetic rock with slippery hard plastic. The texture of these holds is quite like outdoor rock, allowing hold shapes that would be dangerous with a more slippery material.
Outdoor-only handholds mass produced for children's play equipment are usually manufactured from durable plastic. These holds are too slick for most climbers, but they are good for play sets because they are sturdy and weather resistant. Outdoor holds are made out of material with additives that prevent color deterioration due to UV exposure - untreated holds will turn pale brown under extended exposure to sun light.
Nicros, a hold company from the midwest U.S., is currently developing a corn and soy based resin. The goal is an environmentally friendly hold material that is also light and durable.
In an effort to improve the durability of climbing holds, many materials have been experimented with, including a line of thin, hollow fiberglass holds made and patented by Nicros called Extreme Hold Technology or EHTs. These holds are incredibly light, and extremely strong. If the holds are used properly, they hold up quite well and are interesting to climb on as they make a hollow noise when they are grabbed. Routesetters like them because they are light to carry to the top of the wall. Nicros has more recently begun making volumes using their Extreme Hold Technology. They are embedding T-Nuts in the handholds so additional handholds can be bolted to the main handhold.
Currently most commercial holds are made of polyurethane (often called urethane) or a polyurethane mixture. Polyurethane is lighter, more flexible, and less prone to chipping and breakage than resin or natural materials. Like resin, polyurethane mixtures can vary, and different mixtures have different textures and strengths. If the polyurethane is too soft it will split apart when the hold is tightened, or the bolt might get pulled through the hold. If the polyurethane is too hard it will be brittle like resin. Polyurethane holds do not hold up as well when exposed to the sun and rain, so they are not as good for permanent outdoor walls as plastic or resin holds will be. Nevertheless, for the time being polyurethane is the leading hold material.
Types of Holds
A foothold is any hold that is stepped on. Footholds can be any variety of shapes, however they are usually quite small, providing just enough surface to place the toe of one's shoe on. They are sometimes referred to as "foot chips", "footsies, "jibs", "nubbins", "edges" or "nibs". These holds are often of the screw on variety to allow for a lower profile.
Handholds are any holds that are grabbed with the hands. The majority of holds on a climbing wall are usually intended to be handholds, though they may be stepped on as well. Handholds are categorized by their primary features.
Positivity is an indication of how easy it is to maintain contact with a hold. The more outward pull the hold can sustain, the more positive it is deemed. If the hold has a large lip on it and therefore would be easy to grab, the hold is considered very positive. If the usable surface is flat and comes into the wall at a 90 degree angle it is no longer positive. Any angle greater than 90 degrees is considered slopey.
The term "jugs" has dual meanings in the climbing world. One meaning is size based—jugs are traditionally large holds. Most jugs should have space for both hands to fit on the hold. The other meaning of jug refers to a hold's positivity. A hold that is called a jug should be fairly easy to use, meaning it is either a very positive hold or it is a flat hold on a less than vertical wall (slab). Because they are easy to use, jugs are often found on beginner routes, warm-up problems, and steep walls. Jugs are also commonly used as resting or clipping holds on routes.
Mini-jugs are holds that are positive but much smaller than traditional jugs. They are usually intended to be held with one hand only. They are useful because they are easier to carry in a bucket than big jugs and they use less material to manufacture than larger holds do (so they are more cost effective).
Slopers are the least positive of the handholds. They slope down away from the wall with generally a smooth surface, therefore requiring the climber, for maximum friction and in order to gain maximum effectiveness of the hold, to use an open handed grip and push inwards. These holds are usually considered more difficult and are typically reserved for advanced routes.
Pockets are holds that have a small opening, only allowing the climber to hold them with one to three fingers. Pockets can be shallow or deep. One fingered pockets are called monos, and are considered extremely stressful on the tendons. Finger strength must be trained in order to use pockets effectively. Though monos are the most dangerous, all pockets load only a couple of fingers, so climbers must be careful to avoid injuring their tendons. If the edge of the pocket has a sharp radius it will feel more positive but also more uncomfortable. A smooth radius on a pocket is generally the most comfortable to climb on.
Pinches are holds that have two opposing faces which must be pinched (usually by the entire hand, with fingers on one side and the thumb on the other) to grip. Technically, any hold in which the use of the thumb in opposition improves the hold's positivity is a pinch. Pinches require significant hand strength to use, and are usually used on more challenging routes and boulder problems.
Crimps are usually small, slightly positive edges that are just deep enough to fit the tips of fingers into. A technique called "crimping" is used to gain maximum adhesion to these holds.
Volumes (sometimes called piggy back holds) are an extremely large type of hold that any variety of holds can be attached to. The volume is attached to the wall, and it has pre-placed t-nuts in it to which other holds can be attached. Volumes were at one time made from wood, but now they are also made in a variety of materials (including fiberglass, coated wood, resin, urethane, and moulded plastic) by several climbing companies. Volumes are especially prevalent in Europe and on the World Cup circuit, where sometimes entire routes will be constructed from gigantic volumes. To imitate these textured World Cup volumes, sandpaper can be placed on homemade wooden volumes to create texture and allow climbers to make use of the volume's features.