Torsion spring that keeps the blade clamped in place
Had to find out the hard way but in the end the best way. To replace this spring involves inserting one end of a coiled spring in one hole and inserting the other end into a hole you cannot see or get access to unless you remove the reciprocating shaft from the main gear housing. You use two sizes of star bits. 7/16 socket. Flat screw driver. Pin spanner to hold the drive gear while you undo the 7/16 nut hidden under the dust cap. After removing the handle and switch ( keep an eye out for part 44; a small spring that fits in a slot of the handle assembly and cushions the battery receptacle ).
Assembly carefully lift the springs and pull the the brushes out half out but keep them in place under the pressure of the spring to keep their position. Remove the three screw that secure the shoe assembly. Remove the rubber boot. Separate the gear case assembly from the motor housing. Remove two tiny screws that open the gear housing to expose the gears. Use a pin spanner to hold the gear still while using a socket to loosen the nut at the other end. ( reverse threads ) if you got this far yo can figure out how to remove the shaft and yoke assembly find the two holes and replace the spring. I needed the type 1 spring for the single position blade holder. There is a type two spring. Your type is on the label.