I have two patents for springs that act on the main screw (spindle). Undoubtedly there are more.
The first is #74025, granted to Linus Yale, Junior, 4 Feb 1868. His uses the spring to apply tension to the spindle to preload the tension of the jaws.
Partial text of his patent: - excuse the errors, this is Google OCR at work.
4 The nature of my invention consists in so combining a spring with the jaws of a vise, and the screw and nut thereof, that an article may be clasped between the jaws either by the force of a spring or by the whole power of the screw, substantially as hereafter described.
In the drawings, the stationary jaw of the vise is represented at a the moving jaw at 6, the screw at e, and the nut at CZ. Around the stem or shank of the screw of gs. l and 2 is coiled a. spiral spring, e, and this spring bears against the moving jaw and the collar secured to the screw. When the vise has no 'article clamped between its jaws, the moving jaw will bear the relation or occupy the relative position in relation to the screw and collar shown in fig. l, and will move towards and away from the stationary jaw as the screw is turned, with the spring always expanded. When one or more articles are placed between the `jaws, and the screw is turned in the direction to clamp them, then, as soon as both jaws bear upon the articles lying between them, the screw begins to compress the spring, and the articles are held by a greater or-less spring pressure, depending upon the strength of the spring, and the number of revolutions of the screw made after the jaws have come in contact with the articles grasped between them. A continued turning of the screw in the same direction will cause the spring to be so compressed that the collar attached to the screw will bear against the moving jaw, (see fig. 2,) and then the article is clamped, as in an ordinary vise, by the whole power of the screw.
The second is #156066, granted to Erhard Schlenker, 20 Oct 1874. This uses a spring to compensate for wear and keep the handle tight.
I believe that the earliest Parkers used a heavy spring wrapped around the main screw to push out the front jaw.
Patent #71498 (issued to Chas Kingsley 26 Nov 1867) is for the adjustable nature of the Parker collar design.
If you look closely at Chas Parker's patent #11137, (20 Jun 1854 -this pre-dates Kingleys' patent by 13 years) it has a collar on the nose of the front jaw. The collar is screwed in from the top, rather than the front as is Kingsleys. 11137 is for the steel slide strengthener.
Who has some old brass balls Parkers out there with a spring and no main screw collar?
JKB