This simple tool changes how tightly XT60 plugs fit together. It consists of 10 sockets whose pin holes vary from 3.6mm in diameter to 3.3mm in steps of 0.0333mm. The holes compress a male XT60 connector's pins, making the fit looser.

To use, put your male XT60 connector on the plugs one at a time to compress the pins until you get the fit you need. Start with the largest hole size, which is marked with the chamfered corner. The hole sizes decrease from left to right and top to bottom (see picture). Be sure to test the fit after each size, and you may want to try each size a couple times before moving to the next smaller. Use pliers as the XT60 plug will be on the reducer very tightly.

In my testing, I found that not all XT60 plugs, even from the same manufacturer and lot, had the exact same fit when put into the same reducer socket, so you may need to use a slightly different final size for each one. All in all, though, it was a straightforward process to get a consistent fit on multiple plugs. If you accidentally make the fit too loose, you can bend the pins back out again to a larger size with a small nail and start over.

Note that if you make the fit extremely loose you may not maintain good electrical contact, which in theory could cause arcing and be dangerous. 

I had good luck printing this model in PLA. A STEP version is included to facilitate customization.