I have had some of these in my Walden collection for years, and often go there to use one. This 1/2" new in box was one of the ones missing from my set. As you can see, the head is split and slightly larger than 1/2", you insert the bolt/nut and slide the sleeve down to tighten it and they will not fall out. The last picture shows it holding a 3 1/2" bolt.