Summary: Lay square on block to check for squareness and alignment of slot. Use two hacksaw blades side by side to redress the slots. Use the edge of the square as a guide. Choose your favorite design, then mark the block accordingly (See Figure 1). Lay car body on the side, then gently drive the axles into the grooves within 1/4 of the axle head. Axles
Image Dimensions: 500 x 117
Image originally found here.