I have attached a pdf file showing the calculation in question. The 2 views in the pdf are section in the same line. When the operator presses the thumb lever, the pivot shaft rotates the pusher lever which in turn rotates the tooling. The tooling is forced open via the compression spring. My question is, how much force will the operator need to exert to compress the system, and does anyone know if/what OSHA has to say on how much a human thumb can/should push? Thanks in advance, and if any further dimensions/info is needed, let me know, I hope I gave way more info than needed to calculate this. Edit: For ease in calculations, assume 0 friction and ignore the mass of the levers and tooling adding to the gravitational torque of the system.