These are the same as used on many tanning beds and are designed to be used through a 1" x .5" square hole. Internally shunted (both pins are joined), there are two holes for connecting to solid wire, 18-22 gauge, mounted through bottom of holder. Bi pin configuration is designed for T8 or T12 lamps of any length. Actual unit may vary from shown, current unit has no moving parts.

Generally speaking, the other lamp hold (surface mount) is the preferred holder for most projects since it doesn't require a specific sized hole to mount through, but this lamp holder works better for some applications, particularly where the holes already exist.