The following was originally intended as a sidebar in Gary Katz's survey of plunge routers, "Taking the Plunge," in the December 2001/January 2002 issue of Fine Homebuilding. Regrettably, we had to cut this sidebar from the article for space reasons, but we're happy to be able to present it on the Web.
Most small routers are equipped with only a 1/4-in. collet, but most routers 2 hp and larger are equipped with 1/2-in. and 1/4-in. collets, or a 1/2-in collet with a 1/4-in. insert (see the photo above). If you frequently change between 1/2-in and 1/4-in. router bits, consider buying a router with separate collets, such as the Makita RP1101, Bosch 1613EVS or Porter-Cable. The Porter-Cable and Bosch collets are connected to the nut with a c-clip; when the nut is loosened, it pulls the collet with it. No messing with frozen collets. On the other hand, the 1/4-in. inserts are smaller, easy to lose, difficult to install and they can be poorly machined; I even cut my finger on Hitachi's insert.