I got these with some 2.5 inch adapters for an Apollo 4200 large format drive array. They work well with the adapters and now we have SSDs installed as drives in the unit. The caddy is a tiny bit snug, not the best fit, so you'll have to wiggle them just a little as you slide them in. It is perfect caddy to adapt 2.5 hard drives and SSDs for HPE servers and Apollo arrays-but you will always need the adapter, the caddy itself is a 3.5 Inch. Verdict: Fit for purpose for our use. Saved us from buying expensive HP 3.5 inch drives and were able to utilize some SSDs that had been lying around from a previous project.