This is a military surplus flip mirror. It will require some work to adapt it to telescope use and TLC to clean up.
The first surface mirror, about 2 cm square, is operated by two levers. One lever flips it up to viewing position, the other trips it so it folds down out of the light path. It appears the angle of the mirror can be adjusted quite precisely, as it seats against a finely threaded screw.
The eyepiece hole at the top or the unit is 1 inch in diameter, the front hole 1 3/8 in. and the rear hole 2 in. ID. The unit is 1 7/8 in. thick and the main body is a bronze casting.
$10US plus mailing.