This is a Replacement Screw Set for the OS .61 SX-H & .61 RX-H Heli Engines. / / INCLUDES: Six 3.5 x 15mm socket head screws (head screws) / Four 3.5 x 8mm socket head screws (backplate screws) / / REQUIRES: Use a 3mm allen wrench to tighten/loosen screws, / JBN 4.7.94 / ir/jl