My blocks are 2-3/4 by 2-3/4 by 1-3/4 (approx, but close). I bought a set from Mar-K (they've been great - I bought a whole bunch of bed stuff from them), and another mfg., and they're pretty much identical. The bed cross-sills sit 2-3/4 above the frame, so you can figure out the rest. Don't forget there are rubber pads between the wood and the metal too. I put the pads between the wood and the frame...don't know if that's exactly right. I must have had some tweak in my frame, because I ended up having to put an extra rubber pad (or two) on one corner, and no pad on other corners, to get the bed to sit straight and level compared to ground level. Yeah..the first cross-sill forward of the rear sill has a set of blocks - same dimension I'm pretty sure - too.
