Here's a simple way to consistently control cut depth when using a backsaw. The 9" long aluminum rail is lightweight and easy to attach to either side of the blade with a high-friction magnetic strip. The stainless-steel rods give the rail a 2 3/8" range of adjustment.
The two clamp knobs, with rare-earth magnet bases, register against the spine of the saw; simply tighten the brass knobs to lock the rail at the desired cut depth. A reliable aid when a precise cut is needed.
Made in Canada.