Pogo pins are little spring-loaded contacts, very handy for making jigs, or making momentary (but electrically solid) contacts. We use them by the dozen for making programming and testing jigs but they're handy also if say you want to JTAG program a board that you cant solder headers to - just shove these thin contacts into the programming cable and press it onto the contacts.
These particular pins are (in our opinion) ideal because they are skinny enough to fit into proto board or perf board - they have a 1.0mm/0.04" diameter body (the gold part) but the spring contact head is 1.5mm (0.06") wide. The uncompressed length is 16.5mm/0.65", compressed is 14mm/0.55"
Check out our tutorial on how we make pogo-pin jigs!"