Transistors can be incorporated into the miniTesla system without a socket. You bend the legs to the side and clamp them at the top of the spring contacts (see the manual for instructions). However, a more convenient way is to use this socket. It is a small female header with a hole spacing of 1.27 mm (0.05") arranged in two rows with 5 contacts each. The outer four contacts on each side are electrically connected, as are the two middle contacts. This allows you to insert transistors with leads spaced at 2.54 mm (0.1") or spaced at 1.27 mm (0.05").