Lines of Effort
Sub Effort Hardware
Sub Effort Hardware is an attempt to solve the wrong size hole problem.
If you look an an AR lower receiver, you'll see several round holes. 5 on each side, in fact. There's one on each end that are the same size - those are the lug pin holes to hold the upper receiver. There's two small holes for the trigger and hammer pins. And there's a big hole for the safety.
Unfortunately, none of those 5 holes match the standard size of holes in plastic bricks. This has been a concern of ours since we started this project. However, there is a solution. Bushings.
This is not a bushing. Thanks to Wikimedia Commons.
It turns out that a bushing is a kind of plain bearing. What we are going to use bushings for is to adapt our different size holes to the largest screw that will fit in the smallest hole. Take a trigger pin for instance. A regular AR uses a straight round pin to press fit through the side of the AR receiver, through the trigger, and into the other side of the AR receiver. The standard trigger pin is too small to fit in a standard size brick hole, so it would just fall out. What we will do is use a small, thin screw the same diameter as the trigger pin, and use two bushings to adapt the small screw to the larger brick holes.
Whaddabout the big lugs for the upper receiver? There, the problem is opposite the trigger and hammer pins above. The lug pin holes are larger than standard brick holes? What to do? We again use the largest screw that will fit the smallest hole - in this case, the brick hole, and use a bushing inside the lug hole to adapt the screw.
Who sells this stuff? Well, your local hardware store will - or you can go to these folks. They probably have what we need in stock - we just have to figure out what we need.