SPA Steering Wheel Quick Release System?

[dreamscape]

Need some help regarding the SPA Steering Wheel Quick Release System. Can somebody tell me which one Ariel uses on their Steering Wheels as standard, need one for a spare SW and I´m a bit overhelmed by the extensive offer on the site: http://www.spa-uk.co.uk/design/steeringquickrelease/
All i know is that it should be a 20mm Hub and yellow colour:-)