Ralph Haus
Tech Sergeant
Understood. Just surprised at the seamingly random pattern, almost like each had a purpose, location wise, at one time. Interesting.They are called ferrules and, yes, they are for fixing things to the wooden shell. The fuselage is only about 9/16 inches thick and mostly balsa so there's a need for a more solid base where attachments need to be made. A 3/4 inch hole is drilled thru the inner plywood skin and balsa, stopping at the inside of the outer skin. The ferrule, which consists of a 3/4 inch diameter bakelite cylinder with a threaded brass insert all glued to a thin birch ply disc, is then glued into the hole. The back of the disc receives glue as well and is then nailed to the inner fuselage skin with 1/2 inch long brass nails. The threaded brass inserts are designed to receive British 2BA or 4BA bolts.