Used on transmission, mechanical, helicopter: 1615-01-435-3720. seal, plain, aircraft (navy) material rubber compound is fluoroelastomer (mineral -filled, viton fluorel type) ; seal assembly has wire diameter of 0.023"; coil diameter of 0.125"; spring free length of 29.622"; tension 26.50 oz; deflected length of 30.191"; a.i.d. of 9.406" passivate spring surface treated