The internet is… interesting. There is so much information out there that it is almost impossible to find it. But sometimes I find something which isn’t what I look for, but which nevertheless grabs my attention. Like IS 7371.
On the surface, just a dry government publication defining the acceptable standards for stainless steel safety razor blades. But once you start looking through it, you realize that it is a wealth of very specific information that can be interesting for anyone who are tying with the idea of making a safety razor. Or just happen to have a general thirst for esoteric knowledge.
Like this page, one of the earliest in the pamphlet, which rigidly defines the proper size of a three hole razor blade. Which means that we also get a rigid definition for the proper size for a three pin razor head.
Yes, it is a “boring” technical drawing of a three hole razor blade – but it tells us that if we’re milling, casting, or 3D-printing a pin type razor head, the center of the pins must be 12.735±0.165 mm (i.e.: just over half an inch) apart to be centered in the holes. And the pins can’t be more than 5.60 mm (a little under a quarter inch) in diameter.
And slightly further in the document we find another drawing. This ones gives all required measures of a slotted blade.
And this is great stuff, because this isn’t something some random government clerks in India has dreamt up all by themselves. This is based on the blades that have been manufactured across the world since King Gillette first patented his original three piece razor. A blade made to this standard will fit any standard double edge safety razor, new and old. And conversely, a new razor made to fit a blade made according to IS 7371 will accept any double edged blade made anywhere.
IS 7371 also has a lot of other interesting information. Well… interesting if you like to nerd out, that is. Acceptable levels of parallelism. How many nicks each edge can have from manufacture. Allowable size of said nicks. How thick or thin a blade can be. Hardness rating and flexibility of a finished blade. And how many shaves a blade should last for.
That is at least six, by the way.
And the appendixes also includes a section on how to test performance. Some selected quotes from that section:
The test shall be carried out on 24 ± 2 hours old human “stubble”.
The blade shall befitted to a safety razor conforming to IS : 7370-1974 and the operator shall shave using his usual shaving technique with shaving soap conforming to IS : 5784-19701. The operator shall also follow the guidelines for the use of the blades given by the manufacturer of the blades.
blades and shall be required to evaluate the performance of three blades from the packet. With each blade the operator shall be required to shave on consecutive days till the blade has become unsatisfactory (see B-4.1) for use.
An operator shall grade the satisfactoriness of the shave ( with regard to smoothness and closeness of the shave ) on each day by awarding points in a scale of five.
Clearly I need to be more methodical in my blade evaluation…
You can read IS 7371 over at archive.org.