HTP keys are made of stainless steel so they wont rust. They have rounded ends and are fully deburred. They are also tumbled for a perfect fit.
 
The 1/4 x 1/4 key has 2 uses. It works as an impeller key and also doubles as the key we use with our long inducer (HT-HS500L). The 3/16 x 1/4 key soley fits any brand of standard inducer (HT-HS500S).