If I remember correctly this is to remove the "hammer rebound block" in a S&W revolver? Anyways, I only used it once before I sold my Smith. I tried to disassemble once without it and highly reccomend the tool. Purchased through Brownell's, cost about $25 including shipping. Like new condition. Sell for $15. Or trade for Butler Creek STEEL LIP 25rd mag for Ruger 10/22.