Thanks you guys for getting back to me.? I suspect there is something fairly complicated going on here.? I have two machines that I think are both no.3s: a first that I found in an antique store in rural IL, about 1873 as I recall (I don't have the serial no. handy right now); and a second, bought for parts, serial no. 651,408.? I have removed and cleaned up the presser-and-piston (part 24) from each.? They are not the same.? The piston portions are identical, but on the first machine, the presser foot extends downward 0.525", the total length of the foot is 1.425", and the interior width of the glass opening is 0.420".? On serial no. 651,408, the dimensions are 0.450", 1.230", and 0.420", respectively.? So the parts are clearly not interchangeable, even though it looks like the same glass insert would fit into each.? And it seems that each would require its own, different glass insert - at least each with the needle hole drilled in a different place.?
As additional observations, the two pressers appear to have close to the same distal (toward the back of the machine) offset from the center line of the piston, though in the one from the first machine it may be a bit larger. They seem to have identical patent markings stamped into them.? The difference you can see with the naked eye most quickly is that the hole-and-slot for the insert-removing tool is much longer on the part from the first machine than the one from serial no. 651,408.? The total length is 0.210" on the first part, but only 0.110" on the second - on the second part the length of the slot is just about equal to the diameter of the hole, but on the other it is clearly longer.
I am wondering if these differences are changes in the factory design over time, or whether they may reflect that some W&W curved needle machines on sale on sale at the same time were somewhat more robust than others, as is sometimes asserted.
Carl
