Two hands are not enough to build a model, because one of them has to hold the part. Stands and clips take that job over: pegs and clips grip small components while they are sprayed, racks and frames keep sprues upright and visible in one place, ball-joint and bench vices lock a model at any angle, and handles with a grip let you turn a figure or a sub-assembly without ever touching the painted surface. None of it is glamorous equipment, and all of it quietly decides how much of your paintwork survives being handled.
Most damage happens during handling rather than during the work itself. A part held in the fingers picks up moisture and grease, flexes under pressure and shifts as it is glued. Clamp it into a holder and you can work with both hands, see what you are doing, and choose the angle by what the job needs rather than by where your hand happens to be.
The most used group. A small part is clipped, sprayed and parked in a stand to dry untouched. With a larger number of parts it pays to have more clips than you think — the full complement of one model will swallow dozens. They work alongside an airbrush, where a part needs to be turned freely.
These have an ergonomic body and a top face the part or figure is fixed to. Your hand holds the handle, not the model. With figures it is effectively standard, because otherwise you cannot paint a face and rotate the figure at the same time.
Bench vices with a ball mount let a model be tilted and left there. Anyone dealing with an underside, running gear or an interior appreciates it — working in an unnatural position is exactly what spoils results. Large models need a solid base so the holder cannot tip.
These hold sprues upright and visible, so you can see them instead of rummaging across the bench. It looks like a luxury, but on a kit with many sprues it saves real time and cuts the chance of grabbing the wrong part.
A brush should never lie on its bristles or stand permanently in water. A stand keeps it at an angle that extends its life — the detail is in brushes.
For large and heavy subjects it is worth moving to a sturdier solution from the workbench.