The first picture in Fig.1 below shows the front of a block plane by Tower & Lyon illustrating the simplest of mechanisms. Here the knob is loosened, and manually moved along an elongated slot to adjust the size of the planes throat. The Ohio Tool Co. also produced their own adjustment mechanism in the form of a tabbed lever. The lever included a pivot which is seated in a small inlet in the right side of the hole through the toe. When the knob is loosened, and the tabbed lever moves, it pivots about this point, moving the entire knob (and throat plate) backwards or forwards.
In the early 1900s, Sargent & Co. introduced their own adjustment mechanism in the form of a cammed adjuster (Patent No. 818,472, 1906). These cammed levers were unique to Sargent and hence help identify any clones produced by Sargent for other companies.
These cammed levers are often seen on Craftsman block planes, designating them manufactured by Sargent. The mechanism is comprised of (i) a mouthpiece which has two lugs, and an upward projecting machine screw; (ii) a disk with an eccentric cam on its underside, and finger pieces which project from the top; and (iii) a clamping finger nut. By loosening the nut, and moving the disk via the finger pieces, the cam interacts with the lugs on the mouthpiece, moving it forwards or backwards.
Millers Falls went a more traditional route and used the eccentric lever very similar to that of Stanley.