This is a 4-pin Socket Spanner Tool. Two-sided with 20mm ID (25mm OD) 4-pin spanner on one side and 24mm ID (30mm OD) 4-pin spanner on the other side. Double ended, each end has 4 pegs. Internal size of the pegs at one end is 24 mm the other end is 20mm. A 1/2" drive is required to use it.