The “Liberty Bells” are unique for a number of reasons. Firstly, because they are made from steel, and as such as are considered “unbreakable”, and secondly because of their unique blade holding and adjustment mechanism. There are two cast metals inserts which are riveted to the bed of the plane to facilitate the addition of the (i) front knob, and (ii) the plane handle and frog. These sub-structures are cast (solid) rather than pressed to provide much needed weight to the plane – even though “lightness” was one of their advertising values.
The patent invention (No.176,152) was the “device for holding and adjusting the cutting iron”. The purpose of the invention was to “cheapen the manufacture, and produce a simple, sure, and effective mode of adjusting and holding irons”. However it was never adopted beyond these planes. The central idea is to adjust the blade by means of compound levers and a rocking spindle. Depth adjustment is achieved by means of raising or lowering a two-pronged thumb-lever on the side of the plane, which moves the blade up or down. Whilst this makes for quick adjustment whilst working, it lacks the ability for fine adjustment, or even locking the blade into position.
The original patent showed the thumb lever attached with a screw, something that was later changed to a ball-and-socket type joint.
As for the blade and chip-breaker, they are held together with a special screw that extends into a “spur” at the back. The spur or little plate fits into the groove of the depth adjuster. Only Liberty Bell planes have this particular mechanism. In the earlier version (Type 1) of the plane the spur is attached by means of a slotted nut, whereas later versions (such as this plane) were attached by means of a hex nut.