Netgear ReadyNas 3D Printed Drive Caddie 2120, 2120 v2. 2304, 3130, 3138 Will fit the below models: (Rack Mount Units) ReadyNAS 2120, 2120 v2. 2304, 3130, 3138, 3220, 3312. 3312 v2, 4220, 4312, and 4312 v2 These caddies don't have locking mechanisms but have a good snug fit! Note these caddies only accept 3.5" drives only. (They will not accept 2.5" drives) Included: 4x 3D Printed Drive Caddy / Tray 16x Screws