Gary, my BF is a safe queen. I just wanted something unusual to look at when TV gets boring, like now when the Chiefs are kicking the Texans' butts.
So I can't give you a useful answer. Sorry.
BTW, the thumb notches were not on the BF when it originally came with a double guard (of course). They were added when Wayne sent it back to the shop to remove the upper guard , and at no additional cost to me.