I designed these when building a lot of shelves. I made the first set from wood about twelve years back. These are the 3-D prototypes I made copying those wood versions, and as I learned to operate a 3-D printer. They took about four hours print time for each two piece jig.
Used in pairs (i.e., set the first to the opening size you require and lock it in place, put the second against it (the two back to back), then adjust the height of the second to the first and lock it). Once set up, use to position shelves without worry about varying the height of shelves, or having to support them while securing them.
They can be set for shelves about 9-1/4" to 15" high.
I could destroy the prototypes and just have the final version, or I let you have these, minus the hardware (missing the jig knob(s), washer(s) and screw(s)), or you can toss in five bucks a jig for [a] functional jig(s).
If interested and debating the horrible cost, consider pricing 1/4-20 screws, washers and jig knobs, and that you cannot buy these, unless you copy my design, or I sell them, which would run about $34.00 a set.
These are in Desert Aire, Washington. That's about 1 hour from the Tri-Cities, which is, so to speak, next door to Mattawa, Wash. To those who'd ask, no, I won't meet you in Richland / Pasco / Kennewick, or part way. Too many headaches trying to do that in the past. It'd be better for me to throw them in the PLA bin for recycling, or donate them to Habitat.
Your most likely way of contacting me is, actual phone calls, or email. To be honest, I don't live on my phone and have been known to forget it in the shop, or car for a day or two. As such, I may not see a text for a couple days, if at all.