The mechanical characteristics of the RAM expansion DIMM are given in the JEDEC specification for the 168-pin 8-byte DRAM DIMM. The specification number is JEDEC MO-161-D; the specification is available from the Electronics Industry Association's web site, at
http://www.jedec.org/download/freestd/pub95/mo-161d.pdf
The maximum height of DIMMs for use in the iMac family of computers is 1.50 inches.