-6” long, can be cut down to whatever length works for your particular grinder and/or work piece
-designed for small jobs like making a pocket port smooth or for blending in valve jobs
-for use on aluminum and steel
Dave’s take — I use the 3/8 burr for blending pocket ports and valve jobs.  I would advise not using it to port aluminum, it can be used to blend in small areas.  I highly recommend operating at a slower speed when grinding on aluminum and use lots of lube because it will load up and take away from the finish.  This burr is not intended to move material and doing so will cause the tool to load up on aluminum, and will leave bumps because it’s not the right diameter or cut for porting.