Inquiry about measuring for the Steelworxx Tube Jacket 02

I’m considering buying a Steelworxx Tube Jacket 02 down the line, but I’m struggling to find clear info on how to measure. Dietmar told me to “measure the circumference of the penis behind the acorn when flaccid”.

I used a string and got about 9cm (3.5in). Is that roughly correct for what they need, or did I completely misunderstand the instructions?

Thanks.

Are you aiming to find the size for the tube's interior? That seems correct to me.

Dietmar isn't exactly great at explaining his measurement rules. What he's looking for is the diameter of the shaft just behind the glans. Measure "straight across" rather than following the ridge at an angle. If you have foreskin, make sure to include it in that number. Think of it as the inside diameter where the tube sits on your shaft right below the head.