You are reffering to the "fuhrungswarze" (guidingknob). Note that the G7a(TI) in your foto from the "Wilhelm Bauer" museum submarine, has it's knob mounted backwards.
Q1. The width of the glide in the top of tube (its look about 10 -15 mm)?
I have the measurements, but I can't find them now. I'm going to Herdla on friday, so in worst case, I'll make new measurements then.
Q2. Does this glide fixed within the top torpedo tube reset?
Depening on which type of tube the torpedo was to be used, there would be three different "configurations" for these guiding-/holding-/stop-knobs:
* "Smooth" submarine-tube: No knobs mounted
* Standard submarine-tube: Both the "Haltebolzenwiderlager" (stoppingknob) and the "fuhringswarze" (guidingknob) mounted.
* Surface-tube: Both the "Hangewarze" (hanging-/holdingknob) and the "fuhringswarze" (guidingknob) mounted.
The "Hangewarze" was mounted on the airtank. It's T-shape kept the torpedo in position and ensured that it woudln't "tip down" to early leaving the tube during the launch, risking it getting "stucked".
The "fuhringswarze" was mounted on the top of the vertical fin, ensuring the torpedo didn't rotate in the tube during launch.
The "Haltebolzenwiderlager" was mounted above the enginecompartment, ensuring the torpedo wasn't pushed to far into the tube during loading.
I have attached a photo showing the details of the three different knobs, as well as two photos showing the corresponding T-shaped rail in the surface tubes.