If you are building a Polymer80 pistol frame, a long end-mill can help people remove tabs and the barrel channel block cleanly if they have a drill press or milling machine - these will not work in a hand drill.  I sourced these specialized end mills to help and let me explain the features:

• The 9mm (0.393") cutting flute diameter is ideal for the barrel channel work
• The overall length of the end mill is 95mm (3.74"), longer than the original, and makes it easier to reach down into the barrel channel with a drill press with a big spindle.  
• The end mill is a four flute design to enable a smooth surface cut.  Normally you use 3 mill end flutes for finish machining plastic but since the frame work is very light, I opted for four flutes.
• It has a square head with a center cutting design which means you can do plunge cuts as well as sidways cuts with the mill.
• It's made from HSS-AL steel - W6Mo5Cr4V2Al to be exact - and will hold up just fine for doing polymer frame work
• The end mill descriptor is 4F 9*10*45*95 HSSAL

When using an end mill, please understand they are not the same as drill bits.  The work piece needs to be secure and you remove a little bit of material at a time or your frame is going really want to jump all over the place.  These are not for use in a hand drill.

ALWAYS WEAR EYE PROTECTION! Buyer is responsible for compliance with all applicable laws and regulations.

The price is per end mill and includes a plastic storage case for each.