To briggs credit. the often have 'thread in to check' - and I am seeing more chondas with a decal on the side saying do not screw in. Try ManualsLib - they are pretty good.

Good to hear your sourced the blades MF. I am going to order a set to keep with mine in case I ever wear the blades out (although I doubt it, but I guess they will be NLA in a few years time as demand dries up).