Heat treated alloy tool steel, one inch base fits wrench or bench vise. Thin wall construction allows use without removal of cones and locknuts. The FR-5 has 12 splines that are approximately 23.4mm across.
Product Page: https://www.parktool.com/product/cassette-lockring-tool-fr-5
Manual: https://www.parktool.com/assets/doc/product/FR-5_Instructions.pdf
Video (Do I have a cassette or a freewheel?): https://www.youtube.com/watch?v=iTJ3taJHOn8
Article-Determining Casette/Freewheel Type: https://www.parktool.com/blog/repair-help/determining-cassette-freewheel-type
Article-Casette Removal/Installation: https://www.parktool.com/blog/repair-help/cassette-removal-and-installation