I wanted an attachment point for safety concerns as I’m not sure my OP-Z would survive a drop. The tolerances in the blank plastic module that comes with the OP-Z are tight enough that the add-on is held in without any fastener or glue. It can be pushed in and pulled out with relative ease but will still stay secure when dropped attached to a lanyard.
LEGO Black Angle Connector #1 (32013 / 42127)
LEGO Medium Stone Gray Axle 3 (4519)
Keychain ring
Lanyard