Possibly my favourite Bell-matic is the 4006-6002.  The case is really something special and when combined with the dazzling blue dial of the one I bought back in 2008, a real knockout.  Mine, dating from December 1971, came with a German day wheel fitted to the 17 jewel version of the 4006 movement, a poorly refinished case, and the wrong crystal.  But the movement ran sweetly and all functions worked so off to Cousins for a new crystal, a day wheel swap (not performed by me on this occasion) and a case refinish and polish.  Here’s the case next to the new acrylic Sternkreuz crystal complete with tension ring and the outgoing crystal, a lower profile generic domed acrylic:

A close-up of the case, post polish

crystal being fitted using a crystal press (essential, especially when fitted a tension ring equipped acrylic crystal)

Here’s a side profile with crystal fitted

Isn’t that just beautiful?  The movement before receiving its new day wheel

and back in the case

with back, alarm pusher, crown and stem waiting in the wings

The spring on the right is the case spring that pushes back against the lip around the inner diameter of the case back once that is refitted, thereby holding the movement firmly in place.  These springs are notorious for corroding but this one is clean.

With everything refitted, here’s the completed watch

Lovely.