.626-7" or so, they benefit from a light sanding with 600 emery paper. The small pins look a lot neater than the big honking needle bearings that come with most kits.
If you carefully file or stone the tips of your pins square and use a very hard, square pin punch, the likelihood of slipping off is a lot less. Also, back up the junction of the pin and punch tip with the tip of your ring finger. The pin and punch make a groove in your skin and it acts as a coupler/guide until the pin is almost flush...then you just have to be careful. Another tip is you can drive the pin flush with a 1/8" punch, just be careful not to sink a half-moon in the stock on the high side of the pin hole.