If you have acces to a hardness tester, test a pawl from any make ratchet for a reasonable idea of the hardness you will need.
The type of steel used will also play a part in heat treating. I would stat with 4140 and go from there.
Not a bad suggestion but piss on a bunch of Rockwell. It's not like you're building a part that life and limb is dependent on. You can get a real good idea just how hard it is by hitting it with a file.
The 4140 suggestion is fine except for one little issue. 4140 is typically available in prehard bar stock. Machining it is not that difficult but it's still prehard.
The case hard suggestion is also good but a small part like this would be better off through hard.
So what do you do ??
Well go ask Art of course.

He's got all the answers
Elroy don't think so.
This is what Elroy would recommend: Go get some O-1 bar stock and have at it.
And while Art is looking that up in his Marks, O-1 is Oil Hard tool steel. It's is readily available in oversize, precision ground flat stock. It's relatively soft and easy to machine especially when compared to the 4140. Make the part and fit it for size and function then hit it with a torch till red hot. Quench it fast in some motor oil. You'll end up with a through hard part that a file won't touch and if tested will be around 52-58 Rc.
Elroy would also entertain Art's suggestions if he can keep it civil.
The 24 year old boy wonder is also cordially invited.
Elroy has a substantial side bet on this. No response = draw.
Go ahead, make my day gentlemen.