Maintaining the full thickness of stops for the power hammers is more of a challenge that with the hydraulic forging press. The repeated striking of the stop over time by the power hammer ram die tends to diminish the thickness through cold forging even when they are made from tool steel.
I have made a number of the stops from railroad clips. They are plenty tough but apparently not as hard as the 4140 dies in the hammers. I found this source which suggests they are about 1050. http://forums.dfoggknives.com/index.php?showtopic=16220
To make stops I heat the clips and straighten them out. The hydraulic press works well for that. Next, I forge a tang approximately 2” long to fit the die socket or smaller if I plan to fit a piece of 1” square tube over it to finish the tang shape. Then I forge about a half inch of the tip to the desired thickness and let it get as wide as it naturally gets so there is as much flat surface area as possible without going to extra work.
Under normal working conditions the working end of the die should not take a lot of abuse but, over time, the tips do get a little thinner and 5/8” eventually becomes 5/8”-weak and then 9/16”-strong.
My original idea was to reforge the stop when it became thin, pulling more mass out from the body area into the working area. I’ve done that about four times but, in practice, it has been handier to keep the strong/weak dies and just make a new nominal dimension one when a critical thickness is needed.
The current collection contains about 25 stops from about 16 gauge up to about 1.5”. I have them arranged on a carousel rack near the hammers. There is a secondary rack for about a half dozed stops very close to the primary hammer to hold the ones to be used in the current forging cycle.