These bungs are very low profile.  Overall length is only .500: long. Thick enough to not warp from welding, Strong enough for most projects, Small enough to not add excessive weight to your project. To use them  just drill a small hole ( .510" ), place them in the hole and weld them.  These have a 1/4-20  internal thread. The od. of the bung is .750" The shoulder diameter is.500" The hat thickness is .115"    This is for two pieces. .Use them to mount anything you want to tanks, seats, frames, anywhere you need  1/4 - 20 threads to mount most anything.  Made from (easy to weld )1018 mild steel.