It partly depends on the thickness of the body. With a thin body, a 42mm flush mount may be too deep, especially if you have a trem cavity cover fitted (which may well be recessed on some guitars, reducing the available depth).

The trem claw springs fit on top of the block and so add a couple of mm to the depth. Also, as the trem is operated, the block angles and so may poke down a bit more, as you have the diagonal block dimension to consider. It’s far less a problem (maybe none at all) on a downward trem only set up as the trem plate is only moving away from the body, but certainly needs to be considered for upward bends. But to be safe, you’ll probably need to set the trem about a minimum of 1mm from the body to allow the trem to pivot cleanly, so you gain that distance back.

So to prevent the block/spring ends from ever poking out of the trem cavity or snagging on the trem cover, you probably need a minimum body depth of 42+2+1 = 45mm. Greater if there’s a recessed trem spring cover.

With routing to allow upward bends, the trem plate still sits at the same position at rest on the body, but the more the rear of the trem plate moves downwards as you pull up, pushing the end of the block down as well. When doing pull-ups, a longer block will contact the front edge of the trem cavity sooner than a shorter block, which is the main reason for the shorter blocks. No point having a 10mm recess when the rear end of the trem stops 6mm from the base of the recess because the trem block has hit the front on the trem block rout.


A shorter trem block means the springs have less leverage on the trem and also are stretched less for a given movement of the trem arm, so for a 32mm block, you may need 4 springs to get the same feel as 3 springs on a 42mm block. You’ll certainly need to screw in the trem claw a lot more as a bare minimum.