If you order from a web like like Midway or Brownell's or S&W you'll see that the blades are usually sold in kits with the screw and nut. i would recommend that if you order the parts consider ordering a new detent and spring (if they don't come with the kit...I can't remember). At least one that I changed had the original detent and spring jammed into the screw shaft and I couldn't get it out. I would actually order at least two so when the first one goes flying off into space, you have a back-up. If you're not in a great hurry, I would take the old blade off first and measure the height so you order the right one. I've installed two or three without ordering the special two-prong tighting tool. Good luck.