Gotta add my 2 cents to the thread:
Mark a block of birch or other hardwood with a rectangular grid with
spacing equal to a standard microtiter plate (be creative about the
shape of the block itself). Starter-punch the 48 holes. Find 48
nails (brad-headed, probably) of whatever size you want your spots to
be (waste a plate: test a few nail sizes for the spot size they make to
find a size you like). Alternatively, cut 5-cm lengths of welder's rod
or similar steel or aluminum rod (coat hanger would be fine) x 48 and
even up the ends with a belt-sander. Find the drill-bit size that's
just a pinch smaller diameter than the nails, set the depth-gauge on
a drill press and drill the wood-block in 48 places to the same depth.
Press-fit the 48 prongs. Voila! It's faster than Federal Express and
cheaper than anything sold anywhere.
rapr at med.pitt.edu