OK, I'll bite.
Looking at the Wing attach why are the lower taper pins threaded ? Just for ease of assembly ?
The pins are tapered so as to achieve as much overall contact area bwteen the pins and the stack-up of aluminum that comprises a fitting assembly as possible. Pin fit in the bores is achieved by careful machining, followed by lapping the pins into the bores. The taper helps keep the pins seated in the bores as well.
The nut is just for safety ? How much torque do they need ?
The extra nut is for safety. Torque is 36 inch-pounds (that is all you need). I use 40 inch pounds on mine. It is nor necessary, nor desirable, to go beyond this torque range. This torque range ensures that the through-bolt (14-28 SAE Grade 8, and yes, it is a Grade 8 that was supplied by Ken Brock, as it has longer threads than an AN bolt) never has any loads carried by it, beyond the preload that the torque range entails.
Looks like it could lead to a possible mistake when attaching ie too much load on the bolt , and no load on nut ?
Sure it could, but when installing something as critical as a wing attach fastener, aren't you going to be very careful & methodical anyawy? You could get away with having the lower pins unthreaded (several have done this), and rely in a locknut only, but the combination, per-plans works very well, properly installed.
I assume the taper pin thread was designed for that .
I have made drawings from the printed plans but have no definative dimensions - were any given out for the builder to use or was it required to buy them from Brock ?
The plans give sufficinet information for fabrication - 10-degree taper (inclusive) on the pins/bores, 2024-T3 bare for the aluminum parts, 4130 Steel, heatreated to 125 KSI, and such. Several builders have made their own fitting assemblies over the years - it can be done.
