Of course I spoke too soon, thanks for the reminder, I have never owned a M39 bayonet but had numerous M39 rifles and just never tried any of the earlier bayonets on them, they were all sitting on the M27 and M28 rifles. Wish I had kept the collection together, especially since I bought them all from Roses Department store for $35 each back in the early '90s. Even then, when you could find them the bayonets sold for $50 to $75 each - more than the rifles!
BTW, the M39 Rifle was designed as an upgrade for the FinnishArmy. The Sk.Y also used it as a replacement for the M28/30, the successor to their M28. The Sk.Y M39s were built under separate contract from those of the army.
Might as well read up some more, tons of information here:
The Finnish Area