Elgin Grade 221

Here we can see the center wheel and how it engages, by safety pinion, the mainspring barrel. Next along the train are the third wheel, the fourth wheel (the second hand) and the escape wheel.

This is what they mean by marking the movement "safety pinion". The center wheel pinion is threaded on, rather that riveted. If the mainspring breaks and the mainspring barrel flies in the opposite of normal direction, it rapidly unscrews this pinion which in just a few turns lowers enough to disengage from the barrel. When it does, the train "down stream" is then isolated  and saved from potential damage.

 Assembled and screwed together; the complete center wheel and pinion.

This swing-out case has a stem, and sleeve, then a washer or spacer, then a cap, and then the crown.

Note that the stem on this case is not adjustable.

The movement mounts to a ring that is hinged to the case. The back and middle of this style of case are one solid part.

This movement has a small issue in that when the crown is snapped inward it does not always fully engage winding mode. Vintage American watches like this are negative setting. On these, the snapping in and out is a function of the case entirely. The movement is spring loaded to naturally be in setting mode. pushing the stem in pushes the watch to winding mode and the "snap" holds it there. The snap is a function of a spring in the case neck.

This setup makes cases mostly interchangeable, but to work the stem sometimes has to go further inward, or less inward when snapped in. Cases provide a way to adjust the sleeve in and out so the motion of the stem adjusts to the particular watch.

Here we have a problem. This case is not adjustable, not at all! The sleeve, usually threaded, just sits on a cutout inside the neck of the case. It's position is fixed.

The watch is just going to have to live with the slight engagement issue.

Aside: Swiss style *positive setting" mechanisms, such as modern wristwatches have, avoid this problem by making the snapping mechanism a function of the watch movement. Cases are not as interchangeable, but no adjustment is needed either.

This watch is an Elgin grade 221, 16 size, 15 jewels, made about 1902. 

Elgin Grade 208

Here is an example of Elgin National Watch company's grade 208. It is a big watch, 18 size, with 7 jewels, made about 1903. 

What is a safety pinion? Check here.

Burt's Patent

What is Burt's Patent?

Very early Elgin watches are marked "Burt's Patent".

Burt was Merritt Burt (1828-1849) and his invention, later improved by Moseley, protected the watch train in case of breakage of the click, click spring or mainspring; patent No. 44,161 dated September 13, 1864.

From the History of the City of Elgin, published by The Chicago Republican, 1867:

Another advantage will highly recommend itself particularly to the absentminded. Everybody knows that whenever the click-spring of a watch gets out of order, or the click itself breaks, the entire power of the spring acts directly upon the train, and a disaster must occur somewhere, and some of its delicate parts must give way. Most everybody knows, too, that a thoughtless turn too much with the key will very likely break the mainspring, with a like disastrous result to the train. The possibility of these calamities is entirely obviated here by the peculiar construction of the center pinion, which receives its motion from the barrel wheel, and communicates it through the center wheel to the rest of the train. 

In all other watches, the center pinion and staff are one piece. Through the center pinion of the National watch is a tapering hole, and the center staff is turned with a corresponding taper to fit. A concave or screw washer and a nut hold the pinion up. The staff thus fitting closely to the pinion, there is friction enough between them to prevent revolution, and to carry the train. Should the spring break, however, the recoil, instead of acting upon the train, simply turns the pinion around the staff, and no harm results to the train. This improvement, the invention of Mr. MERRITT BURT, of Cleveland, Ohio, which is exclusively owned by the National Watch Company, is called Burts patent,and alone gives a practical value to this watch over all others in existence.