Skybolt Fasteners 15/32 Drill
The Unibit-1 has a 15/32 step...last step before the final 1/2 step.
Typically, before composites came into being and everything was aluminum, the 15/32 hole (.4687) would allow the grommet to clear the retainer ridge that is .471 to .472 wide by slanting the grommet when you insert it into the panel. The typical grommet has a groove/undercut to accommodate the retainer. We have high shear grommets made specifically for the Vans series aircraft, however, there remains the groove for the retainer.
All this works great on .032-.040 aluminum or composite. Thicker panels (aluminum or composite) do not allow enough insert clearance, thus, a .500 hole (.472 to be exact) might be required....depending on how tight you want the grommets to fit. The standard undercut allows some float in the NS or OS style grommets. By eliminating this float, we are allowing a tighter fit with reduced cowling shift and hole wear over time but we are also required to have aligned holes.
Like everything, perfection comes at a price.
May I add that Skybolt is promoting a 20% sale on
Complete Vans RV Fastener Kits from April 1st through April 26th (end of Sun N Fun). Look for us to be back in 2016 as a vendor with plenty of kits and advice, including cowling mock ups for the RV series. Skybolt provides patented interlocking support plates, our DiamondHead series studs, high shear grommets, extensive how-to instructions. The DiamondHead stud are super hard with a machined facing to prevent galling such that they will look as clean after thousands of cycles as they did in the bag they came in.
Call us or go on line....1-800-223-1963
www.skybolt.com If you have questions, give us a call.
Ned Bowers
RV4, RV8, B17, B24, B everything else, L39, Beech everything, Cub.....more Vans...time for a 9....older.