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Gillette's TTO (1947-1968). Imperial Vs. Metric and the mistery of the blade gap.

Lately, I've been studying a lot about Gillette "One-Piece Razors". I'm actually redacting an illustrated handbook detailing the many variants inside the same model through the years.

There is a data that puzzles me: blade gaps. The measurements I've found online seem to be all over the place. I have no way of measuring them as I don't own many of the models. Also, as stated on Razor Emporium page, ideally the measurements should be taken on NOS razors as you'll never know what could have happened to a 70 years old used one.

I generally stick to the shave-wiki chart but even there I see some incongruences.
Let start with a table regarding Gillette adjustables: the numbers are expressed in inches, where "22" stands to 0.022 inches.

Dial position No. 5 on Fatboys and Slims was set by Gillette at 0.032 inches or 0.81mm by the metric system.

(This has been already discussed in the past, see Gillette Adjustable (Slim/Fat Boy) Blade Gaps)

Now, how do those raw numbers compare? I compiled another table based on the measurement on the shave-wiki:

This leads me to a degree of confusion. If modern razors' blade gaps are set following a metric system, a Razorock GC .68 is set at .68mm and a Rockwell plate#5 is set at .69mm. Clear as water!
But Gillette razors were set using the imperial system and the measurements found online are all over the place. I mean, they should follow a progression if converted to metric, even if we consider other steps:
0,015= .38mm
0.020= .51mm
0.025= .63,5mm
0.030= .76mm
No Gillettes, apart from the Red tips (US & UK), follow this progression.

Talking about those wonderful little beasts: users compare the shave they get from a 1955-1959 Super-Speed Red Tip to a Fatboy set at 6 or 7. That would be in the .90-.95mm range If we take for granted online measurements the Red tip has a blade gap of .66mm!!!

Now I know that blade gap is just one part of the equation when we consider the "aggressivity" of a razor. Head geometry, blade exposure are other parameters that come to mind. I mean, a Muhle R89 has five times the blade gap of a Fatip Piccolo!
But the Fatboy and the Red Tip shared the same Gillette 1955-1961 "higher profiled head". Same silo doors curvature, same safety bar, same blade exposure. By the mere blade gap the Red tip should feel like a Fatboy set at 3! Is there any red magick involved?
Wow! Here comes a brave guy asking just the right questions. The gaps on the Gillettes.
From what I have been reading on the forums for many years, most users are just generalising. This goes for the TTOs as well as for many Techs. Most guys have 4-5 Gillettes and have never tried the same head design from a different decade etc.
As for the very first table in your post, I think it is wrong. The Super Adjustable on 9 has a wider gap than the Slim and the Fatboy on 9
And yes the data in the Wiki might be wrong because of wrong measurement and because an used razor could have wider gap than an unused one.
@ivan_101 what I think is Gillette was using inches and not millimeters. They started at '25 with Aristocrats, Senators and Ranger Tech and kept the same gap until 1951. In that year they decreased the gap to '23.
In 1955, with the release of the "Trio" they set the Blue tip at '20, the Red Tip at '27 and kept the "regular" at '23
In 1962 they introduced a new low-profile head (Super-Speeds, Slim) and the new geometry made the head way too mild. It took 8 long years for Gillette to realize they had to do something and in 1970 they brought back the gap at '25.
The new old gap (the one they started and finished with) coupled with the lower profile head made the black handle Super-Speed from 1970 to 1978 one of the most enjoyables Super-Speeds ever.
Just my theory of course!
I agree with you. The TTOs gap from the 40s is bigger. They brought back that gap in the 70s for the black handle Super-Speed. Actually the black handles appeared in late 1967 IIRC. I have a 1960 Super-Speed with the higher profile head and the decreased gap. Unlike the black handle Super-Speed I can't get a very close shave with it.
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