https://www.gobilda.com/1309-series-sonic-hub-5mm-hex-bore/

The 5mm Hex Bore Sonic Hub is an excellent option when fastening a goBILDA® component, such as a gear, pulley or wheel to a REV Robotics 5mm Hex Shaft.  The dual clamping setup maintains the balance so that you don’t introduce vibrations in high speed applications. The threaded holes on the 16mm goBILDA® pattern provide for the easy attachment of parts with thru-holes via M4 screws.