Consider the ubiquitous No.9½, built from 1873 to 1973.
The plane started out looking like this, the But there is also changes in the design of the lever cap, changes in the blade depth adjustment mechanism, and markings on the plane body (e.g. Dating a block plane is often less of a science, and more of an art. Type studies on a series of Stanley planes can be found in John Walter’s Antique & Collectible STANLEY TOOLS Guide to Identity and Value, which has a third edition coming out in 2018.
As the top lever is moved right, the blade inserts, when moved back to the neutral centre position, it retracts.
Because the cages saddle is curved to allow for movement, there is also limited contact point between it and the grooves in the blade.
The next form of lever-based mechanism, uses a pivot attached to an integral saddle.
In block planes it is harder to hide markings, so they can often be found on the surface of the adjustable mouth plate, where they would be hidden in normal use, and only revealed when the plate is removed from the plane.
Here is an example, showing two foundry markings, both “S” and “B” – which doesn’t really give any clarity to the situation.
There are some exceptions to the rule, for instance, there is a type study of the Stanley No.103 block plane, and another one on the Stanley 110/120.
Dating (and identifying) block planes is also more challenging than bench planes because the adjustment and holding mechanisms were often more diverse, and parts were exchangeable, e.g.These levers often suffer from overhanging the end of the plane, thereby decreasing their usability as it is easy to accidentally knock the lever and put the blade out of sync.The levers on these pivot mechanisms, often have 2-3 large teeth which engage with the back of the blade.Then of course there is always the problem of someone replacing a part on a block plane with a part from a different era. Some of Stanley’s bench planes had foundry markings on them to identify which foundry the plane was cast in, typically subcontracted by Stanley.This is indicative of the Type 7 planes manufactured from 1893-1899 which has an “S” marking – some speculate this is from the Session Foundry in Boston.The blade either has deep grooves, as found in the a rack-and-pinion like mechanism, as found in the Ohio No.103.