This set consists of 2 springs and 2 long M4 bolts, washers and nuts.
The springs are 6.4mm OD and 25mm long. They are made from 12 turns of 0.9mm zinc plated spring steel wire.
The bolts are M4 x 60 mm socket head cap screws with a washer and M4 nut.
Strong springs are essential to ensuring the filament drive doesn't slip.