Hi. No they don't fall off, and I'll tell you why in a moment, but first, Note these are not regular thin zinc-plated hardware store rings. They are thick, 8mm thick, stainless steel rings. Inside diameter of 36mm, outer diameter of 52mm, and weigh 55g each. so once you can wear 8 of them, you are hanging a solid Pound (454g) of distributed steel on your shaft.
Details: The strap has Snaps. So you begin at the closed end of strap, around ring and press to base of your shaft.
Next, with mine (people may do this in different ways), you add 2 more to your shaft, not in the strap, then the next one (ring number 4) in the strap, between 2 snaps.
What this does is Pulls Up, on the ring that is in the strap, as there are 2 not in strap so that part of strap and snap are pushing against the rings. This Locks the ring in the strap against your penis shaft, and the feeling, once you get used to it, is quite pleasant, some may say amazing...
I am now up to wearing 12 rings, with the strap locked in 4 places, in this sequence beginning at the base of shaft against body: Rings 1-2 before strap. Ring 3 in the looped end of strap, rings 4-5 free, ring 6 in strap, 7-8 free, 9 in strap, 10-11, 12 in the strap.
Around the house, i wear loose boxers so it really hangs. Going out, I wear ergonomic, pouch style briefs so there is plenty of room, and a boxer brief on top. This allows the package to have room to hang, while holding close to body. AND always with the smaller ring in the photo I supplied earlier, as a 'safety lock'. You can also use a few less rings when you go in public...
I made the strap myself using webbing as previously described, and #20 snaps, and a snap setting tool (Osbourne snap setter)... Lee Valley, Marine fabric suppliers, leather suppliers, have these items.
I will post another photo...