I bought this adapter for use with my camera / monopod / ball head. The ball head requires 3/8" and I thought the monopod had 1/4". I found out I really didn't need this because my Manfrotto monopod actually has both 3/8" and 1/4" screws. However, I did attach it just to see how well it fit; very smooth, not rough, fit perfectly. Came off just as easily.
The quality of this is superb. It is well crafted and looks much better than the photo. It is well machined and smooth, appears to be very high grade steel - not cheap metal that's likely to break.
I'll keep this in my bag until I get a tripod. It's well worth the $5 I paid, and still worth the $10 its going for now. My father is a retired machinist, and he couldn't believe the quality. I can't express enough how fine this steel is; it really is worth it. You get what you pay for with this particular product.
This adapter is well built and works well. If you have a tripod with a 1/4in mount and you want to mount a head with a 3/8in receptacle, then this adapter is what you need. I was worried that the adapter might get stuck inside my camera's tripod mount, but is hasn't yet. Further, if it did, the adapter has a slot that you can fit a blade screwdriver into and turn it out again.
Note that you should make sure that your tripod can support a 3/8 head when using this adapter. That is, smaller tripods (which are more likely to have the 1/4in mount) can become less stable with inappropriately sized heads (and cameras) on them, so be careful.
I would have rated it 5-stars if it were 1-2 threads longer.
I had some reservations about the price of the adapter, but this little piece is of very good quality. I have screwed it and unscrewed it several times very tightly and there are no marks of a screwdriver on it. Adapter looks much nicer in real life than on the picture provided. Smooth and shiny. I give 4 stars because almost $10 is still too much for this.
I have an older tripod with a 1/4 mount. As a result I couldn't properly attach my Manfrotto 488RC2 ballhead. This adapter worked perfectly and allowed me to successfully marry the two. Why 4 stars? $4 seems a little pricey to me for such a small piece of metal.