Z limit switch holder (M505 Prusa i3 variant)

This is a replacement Z limit switch holder for the M505-B. The thicker block replaces the front switch holder which was previously too thin to accurately activate the switch when the carriage came down.

The back piece (the thinner one) is designed thinner to save plastic and prevent replacement of bolts. Also includes recesses for captive M3 nuts (I used some spares from the kit, your's may not be exactly the same size). They do need the application of a little force to fit, but just means