How to mount the switch?

[routercnc]

A series of these momentary push buttons has arrived and I can't work out how to panel mount them.

It looks like they are split into 3 parts - I've managed to remove the lower part containing the switch contacts, but the middle and top part are still firmly attached to each other.

I need to get it apart to feed it through the 22mm panel hole. I've removed the white plastic tab at the top, but this does not release it. I've pulled and twisted but don't want to break them. Any ideas?

Edit:
Typical, submitted the post, then worked it out! Well, it might help someone else. Answer is that the central piece has a tab buried on either side, looking down on the part. I managed to prise both of them back with a pair of tooth picks and slid the central bit out.