Bobo, I don't have a Heiland, but an MPP flash replica, which I took measurements from...if that'll help ya'
. Although, I think it might be a good idea to take down a good average for these measurements as this is only a replica and not the real deal, (if you can get two or three other members to chime in on this matter).
Anyway, I came up with <font color="#00FF00">4 & 3/4" for the outside circumference, <font color="#00FF00">1 & 7/16" for the diameter (going across the mouth of the tube from outside edge to outside edge), and the thickness of the metal itself measures in at only <font color="#00FF00">1/32". This might be all you need, but hopefully others will add their two cents to this.
Otherwise, it looks like,..ask for The Spider, and you get .....The Nerf!
