Square Taper Cup and Cone BB Tool
 

4 notches, all 90 degrees apart. As best I can tell I need the Park HCW-5. The one I have with a hook only is a bit small. Can anyone confirm?

This is a lockring? If so, a lockring pliers should work, e.g. VAR-16, Hozan C203, or homemade equivalent.

Lock ring tools for bikes generally have one of two different curves that fit about the lock rings. One for track hub fixed gear lock rings and the other for BB lock rings. The HCW-5 has one large BB curve w/ 3 notches and the other end with 1 notch is slightly smaller in diameter but not small enough for a hub ring. I guess Park wanted to offer some range of fit with the two almost but slightly different curves.

Options are to get a tool with both the right curve and the right notches for good engagement. Or if the 3 notch end would fit the ring's diameter grind off 2 notches. My go to lock ring tool is the HKC one (the one that was called a "Rock Ring" tool when it first came to my attention a few decades ago and now has the correct spelling "lock ring" stamped onto it). BYW a flat blade screwdriver and a hammer can be a make do tool if in a pinch. Andy

+1. If you want to try homemade just get some Channellock style pliers and grind or file down the teeth so you're left with the nubs on the end to look like the VAR and Hozan tools. These tools are more secure to work with on the lockring and less likely to slip and fecker things up than the Park tool.

Pretty easy to make from a cheap set of slip-jaw pliers:

https://content.instructables.com/OR...8JG5KP8FEI.jpg
https://www.instructables.com/DIY-Lockring-Pliers/

nice, good idea!