View Full Version : Starrett Protractor Head - Proper Fit of Blade

Paul Alciatore
06-22-2019, 05:46 AM
I found a Starrett protractor head in good condition a local pawn shop. Just a very small amount of surface rust in a few places, no dings in the working surfaces, all the parts were there, and the paint is not chipped. It is probably a bit old as it does not have the proud Starrett badge that my square has, but the name was stamped on the edge of the base, just like the older Brown & Sharp one that I already have. It did not have a blade with it, but I figured that the 12" Starrett blade that I already had would fit. The price was right, so I grabbed it.

In cleaning and checking it out tonight, I put the blade in and set the angle to zero. I expected the edge of the blade to align with the base. But it was about 25 to 35 thousandths proud. Is this normal?

When I got the B&S from E-bay some years ago, it also did not have a blade and some pieces were missing; the bolt that holds the blade, the spring, and the thumb nut. I made those parts and searched for a blade that fit. I could not find any. So I purchased an inexpensive, Stanley square at the local hardware with a blade that was too big for it. It had a plastic body but the blade was steel. However the edges of that blade were not parallel to the groove so I had to not only mill the edges to a smaller width, but also correct the angle. I assumed that when it was set to zero degrees, the edges of the blade should be even with the flat of the base so I took care to make it that size and it came out perfect.

That is why I was surprised to find that the Starrett blade does not come out even. So, I am wondering what is normal for protractor heads? I mean good ones, not HF or other cheapies. Is it normal for the blade to be above the base? I would think that would be somewhat problematic when they are set to small angles (< 1). It seems that having it even is the only sensible thing. Could my newer Starrett blade and older protractor head be too many decades apart to match? Has Starrett changed their blade width in the past?

06-22-2019, 07:09 AM
I'm having trouble visualizing the problem you describe. Normally the ruler is inserted up through the head at some angle, and in fact the slot in the head doesn't even run to the ends of the straight edge of the head.
Here's a short video you can compare with. It leads to a second, longer one that shows all the various heads/configurations:

06-22-2019, 07:25 AM
Seems irrelevant to me for use as a protractor. Possibly intentional mismatch to: Make it easier to mark small angles and to reduce tolerance requirements at manufacture.

06-22-2019, 08:11 AM
I have a Starrett protractor head bought new roughly 40 years ago. When parallel to the head the blade is about 3/32" above. Even at that it would be possible to mark an angle almost as small as 1 1/2 degree from an edge, without even having to slide the head over just a bit, hardly a common occurrence.

If I ever have to mark out a smaller angle from an edge, I expect I'll manage somehow. If I can't, I'll ask Mr. Starrett for my money back.

06-22-2019, 08:40 AM
I have an older Starrett head, name marked on the edge as you mentioned. I believe that they had two versions, one was cast and the other forged and hardened.

Anyway, I have a Lufkin blade in it and have never noticed any irregularities. I also have the protractor head and the center head which I use with the Lufkin blade.


06-22-2019, 09:14 AM
Curiosity got the best of me, so I had to look at mine. When the head is parallel to the blade the blade sticks out .015 past the head surface.
The blade measures .9995 in width consistently through out it's 12" length.
I guess there was some standardization between mfg's. back then.


Dave C
06-22-2019, 12:58 PM
Curiosity got to me too. The set I have is old. It was my dad's, bought in the late '30s or early '40s. None of the heads, have any id marks and are a dark green color. The blade has the Lufkin logo, and sticks out about .015 from the protractor base, same as JoeLee's.

06-22-2019, 01:14 PM
I have an old brown and sharp head with an unknown blade it it. When set to 0 the blade sticks out around .100 past the base with a blade width of 1” measured with calipers.

06-22-2019, 01:27 PM
My no name cast with black enamel head has the 1" rule sticking out about .025'ish past the base of the head.

06-22-2019, 04:14 PM
I have an old brown and sharp head with an unknown blade it it. When set to 0 the blade sticks out around .100 past the base with a blade width of 1” measured with calipers.That's a lot. I guess if the screw hook that grabs the slot in the center of the blade is long enough you good to go. It seems like 1" is standard blade width.