Magura made molded plastic clamps for M900 back in the day. I guess so you could run Magura brakes with the XTR shifters. I wouldn't be surprised if someone 3D printed some, but those look like the Magura version. Pretty sure a couple of the silly anodized/CNC companies made different versions too.

https://bikerecyclery.com/nos-magura...ds-1990s-rare/

One place I worked had a good sized box full of those things, couldn't give them away. They lived near the pile of 700c Rockshox forks.