This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
The standard Apple II Slot card has 50 contacts, 25 per side, and is up to 2.75" high (not counting contacts). Contact spacing is 0.10". Length varies. About 0.50" of the length can extend beyond the contacts toward the back of the computer. You may be able to find an 'Apple II prototyping board' from a surplus parts seller; however, these boards are no longer a standard item. To get a new board, you will probably have to get a PC ISA-8 ("PC XT") Slot board (or an ISA-8/16 Slot board with the extra contact strip trimmed off). An ISA-8 board has 31 contacts per side spaced the same as an A2 card. From the edge facing the front of the computer, you will need to count down and trim away 6 contacts (per side). It's best to use a real A2 board as a guide to determine pin centering and to decide what to slice off for a good fit in an Apple II Slot. A Dremel tool with a sand wheel is good for this sort of slicing. The best deal I've found on proto boards for Apple II Slot card projects is the 9003 PB from Marlin P. Jones (still offered as of Feb 2004). It's a good length for most applications (5.6") and costs $7.95. The 9003 PB is 4.25" high; so, you will need to cut off about 1.5" from the top to get a fit in most Apple II's. Another approach to getting an A2 prototype board is to 'clean off' and reuse a surplus A2 card. Or, you can slice off the connector pins (plus a bit extra) from some surplus A2 or ISA-8 PC board and bolt the connector to a common rectangular proto board. By: Rubywand