It appears that the knurled part should push or pull... is that part spring loaded?
I found this:
The Marvel lock system is designed to easily be put on and taken off the guitars without the need of - Any special tool -. By lightly squeezing the cap on the lower part of it, the system can be easily locked and unlocked.
Not much help I know.
However, I believe them to be the same as these Zeppelinn ZSL600 strap locks, which I think I read are made by Marvel:
http://www.zzounds.com/item--MUPZSL600
They have a
website but it is under construction. There is, however an email address and a phone number that may offer some assistance.
Good luck