Skybolt fasteners on the firewall
I have used Skybolts on three firewalls and have never used their interlocking flange because there is an easier method. The assembly of a series of flanges isn't so simple.
What is simpler, in my opinion, is to cut a strip of .063 aluminum 2 inches wide and as long is required to go around the firewall. You can do it in two strips, joined in the center. You take one Skybolt interlocking flange and determine your fastener spacing (typically 3 inches) and layout however many fasteners you will need. In minutes you can cut out the fastener tabs on the band saw and with a little filing, or use a 1"belt sander. You attach this continuous strip to the firewall. You measure back a certain distance from the center of where the 5/8" hole will eventually be (where the 1/4 turn stud goes), but don't drill anything. Once the cowl is fitted and laying on the protrusion, you drill a #30 holes through the fiberglass and through the .063 strip. Once the cowl is fitted and held in place with clecos, you remove the cowl and mark the location where the fasteners will be attached, making your own template with three holes in a row 1/2 inch apart. You may consider using a #30 hole only in the center and #40 for the two outer holes. In the end, use an actual fastener (as a drill guide) to finish drilling the two outer holes to #30. When your satisfied all the fasteners are in the correct position, drill the center hole out to 5/8 hole, using a step drill. There can be some assembly and check that all holes are where they are suppose to be. The last step is to drill out the #30 hole in the cowl to 15/32" using a 1/2 inch unibit.
It takes longer to explain than actual do it.
Jake Thiessen
Independence,Or