K and s brass tubing 3/16 external diameter (4.762mm) wall thickness 0.356mm = ID 4.05mm. Comes in 12" and 36"

Mike

Hi Steve, I purchase K s brass tubing from my local hobby shop (Australia) http://www.ksmetals.com/26.html I use both 5mm and 6mm tubes to use 4mm and 5mm ball bearings. With a wall thickness of 0.45mm the internal diameter is 4.11mm and 5.1mm. I use 12" lengths and sleeve them in the next sizes up ...