I have a daughterboard with 3.5mm screw terminal blocks (such as Digikey part # 277-5749-ND)
that has to be connected to the mainboard, with the daughterboard either parallel or perpendicular to the mainboard.
However I do not find any 3.5mm male pin headers (http://www.digikey.com/product-search/en/connectors-interconnects/rectangular-board-to-board-connectors-headers-male-pins/1442672) to mount on the mainboard, so that the pin headers can be screwed into the daughterboard's screw terminal blocks. The closest is a 3.60mm pin header.
What is the recommended way of connecting them together? Using multiple single pin headers on the mainboard spaced 3.5mm apart?
For a one off connection of two already designed boards, take standard cables with 0.1" headers (male or female as needed in your main board), and strip one end/cut in half. Either screw that into the terminal blocks, or solder it into the holes left from desoldering the blocks.
Or you could make some adaptor boards, that have standard 0.1" or 0.05" on one side, and use individual leads spaced 3.5mm on the other. A bit tedious to solder, but a cheap pcb and some breakaway male headers will only cost a few bucks.