Screw-on climbing holds and bolt-on climbing holds are two different types of artificial climbing holds used in climbing walls.
Screw-on climbing holds are attached to the climbing surface using screws that are drilled into the wall. These holds are easy to install and can be removed and repositioned anywhere on the wall as needed. Minute adjustments of the position of the holds are easy to achieve. 2 to 5 screws are
commonly needed to affix a given screw-on hold. "Screw-ons" are cost effective as they don’t require pre-installation of t-nuts at the back of the plywood surface. TNUT's SCREW-ON HOLDS have at least two holes of diameter 3/16" (~4.8mm). Non-self drilling timber screws (i.e: 10G x 30mm to 50mm) are recommended.
-> faster wall building time, cost effective, slower hold installation, screw holes remain apparent (albeit less than 4mm) once the hold is moved.
Bolt-on climbing holds, on the other hand, are attached to the climbing surface using bolts* that are screwed into a grid of fixed t-nuts. The latter are pre-installed at the back of the drilled climbing surface. They are still the more standard method of installing climbing holds in indoor climbing commercial venues despite a marginal but growing trend to move towards screw-on only walls (i.e: on the international competition circuit). Bolt-on climbing holds are faster to install and secure firmly to the wall in one action with the use of an impact driver. In many cases, only an additional set screw is added to avoid spinning holds.
-> slower wall building time, added t-nut cost, faster route setting, neater wall.
Both types of holds are designed to provide a standard method of attachment and a more adhoc, flexible one. The two depends on the specific climbing wall and its intended use.
TNUT's 13 screw-on mini jugs from the MONSTER series (catalogue reference M00007) are our most selling set of screw-ons as they are versatile and can be installed on any solid wooden panels, fences, trees, hangboards, system training walls (i.e: often to place in between bolt-on hold)...
Our 12 screw-on positive small hand holds (catalogue reference M00005) are spread around kids playrooms everywhere in Australia (see the toddlers climbing frames by @littlebiglearning)!
Other popular sets of screw-ons are E00008, E00009, C00012, C00021.
Note that there is a larger variety of bolt-on holds than screw-on holds on the market.
* In Australia, your hardware store doesn’t call them “bolts”, but more
precisely “socket head cap screws”.