Wondering if anyone would know this: are all 18s 17J grade 345's double roller? I notice many have that marking, but some do not. I've seen pics of some that are pretty close in serial number, some marked, some not. Thanks, Ted.

I think I answered my own question.The factory descriptions list them as "double roller escapement".Mine is # 528140, is not marked but I slid off the dust band, looked inside and looks like a double roller to me.I'm thrilled to finally get a real nice 345, appears that only 3000 were made. I've wanted one for a real long time.