A limit switch operating head subassembly mountable at its mating surface onto a switch subassembly in any one of a number of different angular positions and may be detached without any parts falling out. The operating head subassembly has an operating arm pivotable in opposite directions for switch actuation. This operating arm is secured to a shaft that operates cams, rockers and slide members to operate an actuating plunger through a presettable mechanism allowing by-pass in one direction. The slide members are internally compression spring biased threaded members allowing stepless length adjustment. The presettable by-pass mechanism has a flanged plunger on a square pin and a notch in the flange to allow presetting the plunger notch at 90 DEG intervals for switch operation in both directions or by-pass in one direction of operating arm movement. The operating shaft has a seal design that enhances sealing effect under fluid pressure and is smaller so as to use less material. An adjustable coupling mechanism transmits the plunger motion to the contact actuator. The stepless length adjustment of the slide members and the adjustment of the coupling mechanism afford adjustment of the plunger motion relative to the mating faces of the operating head and switch subassemblies, respectively, to afford presetting of switch tripping at five degrees of arm movement.