The problem
These stairs aren't sagging, but there's no way those triangles will hold a nail. Weather makes the steps warp and loosen, it's very unnerving. Stair saver locks them down so there's no movement. The brown staircase shows a Simpson stair angle which is still only attached to the weak triangle of the stringer already cracking off. Old stairs are never at a perfect right angle, stair savers don't need to fit perfectly to work fine, small gaps won't matter.
Stair savers solution
this is a 7/11 inch rise/run
this is a 7.5/10.5 inch rise/run much steeper
While Stair savers are built for a standard 7 inch rise and 11 inch run, it can adapt to whatever rise/run you have. For any loose step you will need at least two Stair savers one at each end.
Stair saver is basically hand-built from solid half inch square steel. Cuts and holes are not perfect and it makes no difference. we barely spray them to prevent surface rust. See this 120 plus year old fence with very little paint left, solid steel will only rust on the surface So paint them more if you want but they're not going anywhere.
Stair saver screws locking down the steps and risers are close to the wood of the stringer so use a long bit holder or two put together. Stair saver takes up about 5/8 inch so if you're screwing into a 2 by step(1 1/2 inch) use a
1 5/8" deck screw to penetrate 1 inch. If later you want to build a new staircase just remove the Stair savers and use them to make new stringers. My partner and i have been rehabbing old buildings in St. Louis city for over 30 years and we've often found steel solutions to wood issues.
