Hi Louise,
Thank you for your enquiry on our website. The diameter of the castor cups should be at most 3 inches and you will need 6 for a single base.

I trust that this helps and if you would like any further information please do not hesitate to contact the office on 0161 437 4419.  Our office hours are 8 am – 8 pm Monday to Friday and 10 am – 4 pm Saturday and Sunday.

Kind Regards

Michaela