This is an Errington 20J Keyless movement for a hunter case by C.H. Errington of Coventry. Bought without the missing case but in working condition.
A 3/4 plate, it has 20 jewels, a cut compensating balance with gold screws and Breguet hairspring.
Serial # 34219, diameter 19'''/43,2 mm and a hight of 7,4 mm