Piet the cush drive spring free length when new is 1 5/8" (41.27mm) down to 1 1/2" (38.1mm) is acceptable. No compression tool is needed, it's probably the clutch you're thinking of.
I am selling some of Robb's (USA) cush drive and clutch nut tools on his behalf in UK/Europe at £22 each. Email me if you want further details.
