Hard drive won't fit in enclosure

I have an old Macbook that I want to use the hard drive (2.5 inch) from as an external. I bought a 2.5 inch hard drive enclosure for it. But it won't fit. There are four pegs on the sides stopping it from fitting.

Was the enclosure too small? Will a different 2.5 inch enclosure work? Is there anything else I could do, or will this project just not work? Thanks.