This is a gridfinity holder for 8 inch calipers - made by Amazon noname brand "Mriuuod". A photo of my calipers is in the post on thangs.com

this uses mattwhispell's model "Gridfinity NEIKO 8in Caliper Holder" as a reference, I only had to remove a small amount from his to make mine fit.

I could not be bothered to try to repair the fillets, I took a rough cut out of the model. This could definitely be improved.

mattwhispell's original model can be found here: https://thangs.com/designer/mattwhispell/3d-model/Gridfinity%20NEIKO%208in%20Caliper%20Holder-838111