Caliper Depth T-Bar

I saw this thing on amazon.
https://www.amazon.com/iGaging-100-D68-Caliper-Attachment-Calipers/dp/B00M78245C/ref=pd_sim_469_3?_encoding=UTF8&pd_rd_i=B00M78245C&pd_rd_r=VE5MT28X073550GZJ0EV&pd_rd_w=b0IG9&pd_rd_wg=7hdcY&psc=1&refRID=VE5MT28X073550GZJ0EV

$18 seems a bit steep for my $17 4 inch caliper. So I made my own. I used a M4 screw for a set screw and a M4 ultrasonic insert. They are available from Global Industrial for $5.00 for 100 of them. For those unfamiliar with these inserts, you just heat them with a soldering iron and they sink right into a properly sized hole and now you have metal threads!

http://www.globalindustrial.com/product/itemKey/30435445

The Onshape design is available here:
https://cad.onshape.com/documents/c5d1c16f1719cb7038a51541/w/0ecade61c7dcd5756392f292/e/f950a21c6f616f9119e69327

Right now, this is only for the 4" caliper but I plan to make a version for the 6" caliper.