In looking at a datasheet for a typical Tyco "500-series" machined-pin DIP socket (e.g. mouser.com 506-508-AG11D), I see that they also accept round pins that are from .016" to .021" diameter, with a .105" minimum length, in addition to .009"x.015" through .011"x.020" rectangular pins.
Mill-Max makes a long-tail DIP socket with pins that have .020" width (can't tell if they're round or not) and .170" length, which should leave .105" or more pin-length under your daughterboard for daughterboard thicknesses of .065" or less, except for the thickness of the solder joints. So they might work if you use a .031"-thick daughterboard. Part numbers for 40-pin ones, at mouser.com, are 575-11143640 and 575-993640. They would have to be soldered on the bottom side of your board.
Mill-Max also makes DIP headers (with .018" pins) that might work better, if you use two single-inline ones. But you'd have to solder them on the top side of the board. You can go to
http://www.mouser.com and search for 575-641591 and then download the catalog page from the link that will come up with the part listing, and look at the last four items on the page. They're a little pricey. So it might be a good idea to look at some cheapo pin headers' datasheets and see if any of their pins are small-enough.
Aries Electronics (
http://www.arieselec.com ) makes some adapters that are just like the ones ericgibbs pointed out. Mouser.com has them, but apparently only up to 28 pins. Their datasheet shows the pins as .019" x .015" x .150". So they might leave .105" for the socket, if you use a .031" daughterboard thickness, depending on the thickness of your solder joints. (But notice that their rectangular pins are larger than the Tyco socket is spec'd for. Typo, maybe?)
Aries also makes some 40-pin machine pin collet sockets that have a .183"x.020" solder tail pin (their "E" version: Aries # 40-6518-10E). But they're "non-stocked" at mouser.com .
If none of the above will work for you, it looks like maybe you should just look closely at the specs for various sockets and headers, and you might find some that would work.
Good luck!
- Tom Gootee
**broken link removed**
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