Our Titanium is Nickel Free, half the weight of Steel, and available in several brilliant colors, without the use of dyes to color it. We only use G23TI Surgical Titanium or 6AI-4VEli Implantable Titanium. Both of these grades have been successfully used worldwide for heart valves, pacemakers, and implants. Circular Barbells are a great design for people who frequently remove or change their jewelry. All Internally Threaded, and can be worn with virtually any piercing. Circular Barbell's are measured using the inside diameter.
Well, I have the entire set (20mm, 30mm, and 40mm) and find the 40mm to be the best of the three. From the time I received my 20mm guy, I have worn one of them for 58 consecutive days (unless there is a metal detector problem, there is no reason to take it off). I have only a single (minor) nit to pick: the design (a pin and one hex-head screw) makes it a bit of a bother to put it on. But, DON'T SWEAT IT; with a bit of patience, you'll get it on and enjoy this wondrous ornament for a very long time. (Why, oh why, couldn't I have had one of these 50 years ago (I'm 71 now)? Sigh.)