Simple delrin jig to calculate engine standoff height & center cowl prior to cutting any holes in your cowl. Spinner back plate when mounted on jig is centered within mounting holes. Rear surface of jig (against firewall) gives you the engine mount surface to drive washer length.

Just use a 15/64" transfer punch to mark holes in firewall and drill after the back plate is centered on cowl and jig is centered. If you try to drill directly from the jig, which is not advised- You would need a 6" aircraft drill and likely gouge or oblong the holes in the jig.

*Note - Hole pattern is not centered in the plate and the plate edges are just rough band saw cuts. Holes were drilled from coordinate dimensions. So true vertical or horizontal mounting is by eyeball and not representative of the plate edges.

Makes for less work mounting and cutting a nice clean cowl.

$20 shipped USPS to lower 48.