Thanks Oily. I did not know that Thosen produced early versions of the enclosed round head. I guess I've never run across these in the wild; must be fairly rare.
Any clue when the open head ratchets first appeared? I noticed the 1958 Thorsen Brochure/Pricelist I sent you a copy of mentioned "The All-New Thorsen Ratchet" and it's features (i.e. open head design... simplicity). Included in this brochure/pricelist were ratchet models 77M, 77J, 77, 77NR, and 79. Could 1958 have been the introduction of the open head design? If so, that would be a fairly short run, ca. 1958-1968 (perhaps a little later).
There are issues I have with dating the start of the open head design in 1958. 1) I have surfaced a 1955 brochure that also has the open head ratchet included in chrome form and with a "dust cover". 2) I have examples of the open head 77 ratchet that pre-dates the introduction of chroming AND the dust cover. It is fair to say at least TWO improvements were made to that ratchet; the cover over the open head, and chrome plating. I can't even conclude the "The All New Ratchet" marketing found in the 1958 literature was covering an improvement I've discussed here (again, I have a 1955 showing chrome and a cover).
Link to thread with 1955 brochure download.
http://www.papawswrench.com/vboard/index.php?topic=9680.0This is the early 3/8" drive 77J open head design that pre-dates chroming and the dust cover.
This is an early round head 3/4" drive Thorsen ratchet (with removable drive plug) I have.
And lastly, there is this early ratchet which is marked 77JA. It is of the open head design, no original chroming, and with a fixed 9/16" socket. It is unclear to me if this was a specialty ratchet, or if it was ONE within the timeline of their ratchet's progression. I will say that of the four 77A ratchets I've seen (and I own two of them) they were all of the 9/16" size. Which leads me to believe it was a specialty socket versus a situation where multiple size fixed sockets were available in this ratchet design. I hope that makes sense.