Solid steel and therefore "last forever". The Inne thread is not quite consistently, at the end (last 1/4 thread) not quite worked out, but ranging from the length of a tripod or similar thickness from. I needed a reducer as spacers on a 20mm long thread, so I remembered that on. External threads are fine. The reducers can be screwed well and tighten with a screwdriver. But with me they think that way. Price is okay.