the smallest lathes are "jewelers lathes" or "watchmaker lathes", which, though often small enough to be held in one hand are normally fastened to a bench. the workpieces machined on a jeweler's lathe are often metal, but other softer materials can also be machined. jeweler's lathes can be used with hand-held "graver" tools or with a "compound rest" that attach to the lathe bed and allows the tool to be clamped in place and moved by a screw or lever feed. graver tools are generally supported by a t-rest, not fixed to a cross slide or compound rest. the work is usually held in a collet, but high-precision 3 and 6-jaw chucks are also commonly employed. common spindle bore sizes are 6 mm, 8 mm and 10 mm. the term ww refers to the webster/whitcomb collet and lathe, invented by the american watch tool company of waltham, massachusetts. most lathes commonly referred to as watchmakers lathes are of this design. in 1909, the american watch tool company introduced the magnus type collet (a 10-mm body size collet) using a lathe of the same basic design, the webster/whitcomb magnus. (f.w.derbyshire, inc. retains the trade names webster/whitcomb and magnus and still produces these collets.) two bed patterns are common: the ww (webster whitcomb) bed, a truncated triangular prism (found only on 8 and 10 mm watchmakers' lathes); and the continental d-style bar bed (used on both 6 mm and 8 mm lathes by firms such as lorch and star). other bed designs have been used, such a triangular prism on some boley 6.5 mm lathes, and a v-edged bed on ime's 8 mm lathes.