Greetings Aussie, and welcome to the ODK Forums. :welcome:

If your machine is an Orion X or XL, the user manual/IPL is a free download from http://www.coxmowers.com.au/operation-manuals/

For those models, the lower yoke and the locking ring beneath it are locked by 'set screws'.
These may have external heads, or be the flush type with a hex socket to accept an Allen key.

Cheers,
Gadge

"ODK Mods can explain it to you, but they can't understand it for you..."

"Crazy can be medicated, ignorance can be educated - but there is no cure for stupid..."