Our Sub Compact “NQI PFSC 17-4 Front Locking Block” is made of 17-4 American sourced stainless steel and precision CNC milled for a higher quality and longer lasting rial system. These are not heat treated to allow the rail to be softer than your slide and to allow the parts to wear overtime while saving your more expensive slide from unnecessary wear and tear. The tolerances are far improved over the standard MIM and stamped parts increasing overall accuracy. Some final honing can be done to achieve a completely flat rail system from front to rear depending on the holes you drilled but isn’t necessary for most applications. See the videos posted under the manuals section if you’re ready to go the extra step towards perfection.