Stanley first offered the little bull nose in 1879 and it appears that no patents were ever issued on the design.
The design is simple with a minimum of bells and whistles.
For over 100 years Stanley as well as other makers offered the little rabbet.
Companies such as Sargent, Ohio Tool, Union Tool and Millers Falls all had a No. 75 look alike and most can be found on the used tool market with a little looking.
The small size makes the plane a very useful addition to the bench. It can clean up a rabbet with ease and will if pressed work cross grain. The top part of the body slides and the mouth can be completely closed or left gaping, shaving eating monster.
A nice advantage for a very inexpensive plane and a big plus for any rabbet.
The cutter adjustment is more like that of a wooden plane than a Bailey bench plane but the design makes it something that once learned, is not hard to do.
Adjustment:
With most planes three basic adjustments are important and the 75 is no exception.
First, adjust the mouth. 
To do this I have found the best way is to set the plane on a thin shim, for example a metal rule, and let the blade project through the sole of the plane.
With the blade projecting through the sole of the plane snug the nose up to the blade and gently tighten the screw that holds the two parts of the body together.
Next, check along the two body sections for alignment.
The sides of the nose section and the main body should be more or less in a straight line. The straighter the better, as it will limit the amount of lateral adjustment required later.
The above is done without the screw cap in place.
With the body sections in line and the mouth nearly tight to the blade, install the screw cap and slide the blade back until it is about where it will be when the plane is in use.
Now, keeping the body screw somewhat loose but firm enough to hold the two sections, tap on the tail of the top section to open the mouth to the desired width.
Tap gently as the sections can move easily and loosen the screw cap.
Once the mouth is set, tighten the body screw firmly.
I use the edge of a screwdriver at first to snug things up, then remove the blade and use the proper size driver to tighten down the screw.
Do not use lug nut torque to tighten screws on planes!
In most cases a firm turn of the screw will hold parts and cutters in place.
The next two adjustments are the lateral adjustment and the depth of cut.
To avoid knocking out the other, these two adjustments need to be done somewhat together - that is, both working simultaneously towards the goal of a well adjusted rabbet.
The lateral adjustment is the easiest.
With the plane held upside down, sight the mouth and apply pressure on the top of the iron to align the edge of the cutter and the mouth.
When properly set, the gap between the front of the mouth and the front of the blade will be uniform all the way across.
For all adjustments, the cap should be in its final position and the screw just tight enough to hold things in place.
Too tight and you can’t move the iron without beating the tool and too loose and the iron will just slide around.
Also, watch the sides of the cutter while making adjustments.
Ideally a rabbet plane iron is exactly the width of the plane body plus a hair for clearance. In reality most blades are slightly wider than the plane they fit. So make sure the blade is centered and projecting equal on both sides of the body.
The depth-of-cut setting for this plane is easier than one would expect.
The nose section of the plane is slightly above the sole of the plane.
This is similar to an electric jointer where the infeed table is below the outfeed table.
The difference in elevation of the two tables is the thickness of cut.
With the sole of the plane lower than the nose of the plane, setting the iron is somewhat simplified.
With the plane sitting on a flat surface, slide a sheet or two of paper under the nose section.
Now slide the iron gently down on to the paper and retighten the cap screw enough to hold the cutter in place.
Holding the cutter on both sides of the body as it is lowered helps maintain the lateral and side adjustments made early.
It is better to have too much thickness under the nose than too little. With too much paper under the cutter the cut will be to light and it is just a matter of tapping the cutter downward. Too little paper and the cut is too coarse requiring that the cutter be moved up and that is difficult to do with much control.
Check the lateral adjustment and the blade side alignment, if no adjustment is required tighten the cap screw and try the plane. Depending on the amount the nose is underground the cut should be quite light and the shaving thin. If a coarser cut is required loosen the cap screw a bit and tap the iron gently downward. If a finer cut is in order, resetting the cutter is the easiest way to go.
After you have set the plane a few times the procedure will become natural and all the paper shims can be used for taking phone notes and the little rabbet for making shavings.
Availability:
The Stanley No. 75 rabbet plane was a handy, inexpensive plane that found widespread use among tradesmen.
Add to that the usability, the long production period plus numerous makers and you have a plane that is readily available today.
New-in-the-box examples can be had for less than $100 and good users run from around $20 on up depending on condition and blade length.
New old stock cutters can be found from time to time and run about $15 to $20 each.
For the money, the Stanley No. 75, is a simple plane that works and won’t break the budget.