This 3/8" collet will enable me to use not just the run of the mill 1/4" and 1/2" router bits and end mills that are so common from other sources. This gives the Porter-Cable router more versatility in the shop extending it's range of use. I use the double ended end mill (spiral upcut router bit is the same but only on one end) which gives you twice the length of usable cutting edge. When one end dulls you can turn it over to the opposite end without sharpening or having to buy a new bit. So now I can use a 1/4", 3/8", and also the 1/2" shank end mill bits and also all the router bits available to accomplish my tasks.