Thread size help

JRSutton · Sep 23, 2015

Just put a new armature in a 6 volt delco generator. Old nut for the pulley doesn't fit.

Here's the spec for the new shaft's thread: .669-20

I'm guessing that's a convoluted way of saying it's metric.

I just need one castle nut for it, and I know they're not all that expensive, but I'd still rather just buy one as opposed to several guesses.

IanC · Sep 23, 2015

.6693" is 17mm, but metric thread pitch is distance between thread peaks 1.0mm, 1.5mm, etc 2.0 would be very coarse thread.

JRSutton · Sep 23, 2015

Right - the numbers really don't make any sense - I assume it's either a 16 or 18 mm, since 17 isn't a standard size as far as I know.

So I was hoping where these generators (and their replacement parts) are so common, somebody might just know off the top of their head what it may need.

I lost my thread gauge long ago. Never really needed it... till now!

TimV · Sep 23, 2015

Actually, I believe the "20" is threads per inch (TPI), the same as most standard threads are measured. From a quick Google, it looks like it's not hard to find--tons of them on ebay or any generator/alternator shop should have them.

JRSutton · Sep 23, 2015

I've been googling it of course - but all I can find is that stupid spec.

Figured somebody here has used one of these armatures before and might just know.

Not the end of the world, I can do the buy-four-times-what-I-really-need shotgun approach.

Of course, I already DID that thinking it was standard. 5/8 fine, course, 3/4 fine, course...

typical - just need a simple nut and it turns into a long expensive process.

It's always the simple things that kill ya.

boler76 · Sep 23, 2015

I ran into same problem, ended up removing the threads and rethreading to a size I could get ??

TimV · Sep 23, 2015

Here's one on ebay--I know nothing about the seller, but there's a bunch of listings for these nuts, you've just got to use the thread size they give you and not get hung up on whether or not it's a standard size.
generator nut

JRSutton · Sep 23, 2015

AH - I never thought to search for the nut itself.

I kept searching for the armature - hoping to find more info. I thought for sure it was just a typical chinese to english nonsensical translation.

Thank you!

Steve@Advance · Sep 23, 2015

What a strange combination! Metric diameter, inch pitch... How crazy is that!

Never measured one before, but it must be somewhat common. If you didn't want to wait for the one on Ebay, maybe a local rebuilder would have one.

Dblair · Sep 23, 2015

that would be a 17mm x 1 mm thread , not a likely thread it's probably a 11/16 x 20 thread .just my opinion .

J. Schwiebert · Sep 23, 2015

If I remember right the old corvair had the same size, but Left Hand threads.

George by Geneva, NY · Sep 23, 2015

Is the bearing a 6203 by chance? That has a 17 mm bore, which is about 11/16 so that could be the nut size. Any good genny rebuild shop should have them on hand or at least get the right one. Remember, ball bearings were sized to metric and tapered are usually in inches. In more recent times, ball bearings have been made in inch sizes.

armand tatro · Sep 23, 2015

Get your copy of Machinery's Handbook out of your toolbox and look at the thread cutting section! There are a lot of charts showeing thread pitches, diameters, speced in inches, mectric, or whatever standard you need! Armand

Hoby · Sep 23, 2015

Try This.

gene bender · Sep 23, 2015

Its 9/16 fine i mite have one would need to check its not metric.

JRSutton · Sep 23, 2015

no, 9/16 definitely doesn't fit - that's what the original one was. This is a replacement armature.

JRSutton · Sep 23, 2015

right but a 11/16 - 20 is .687, not .699 - a minor difference but ... A.) why call it .669 - B.) even if that's what it is, I can't find an 11/16 castle nut.

It's closer to 17mm - but I can't find a 17mm castle nut either!

It's just a very odd size - and I wish I knew for sure exactly what it's trying to be!

I guess I can just order the nut off of ebay - and probably will. But WHY? why on earth would they not just use a standard thread size?

I'm sure they have their reasons - but it's irritating.

gidtex · Sep 23, 2015

11/16-20 thread

Bob · Sep 24, 2015

Oh, for gosh sakes, that's gotta be the most common generator and alternator pulley retaining nut out there!

NOT sure what you are going to do with a "castle nut", 'caus typically there ain't gonna be a hole for a cotter pin in the armature shaft???

IF you can't find one to recycle off of a Delco generator or alternator, you can pick one up at a DEERE parts counter for well under two bucks. (# R11049, Diameter 0.669 IN, Threads Per Inch/Pitch 20 Thicknes. Across Flats 0.938 IN

JRSutton · Sep 24, 2015

Well they might be as common as dirt, but it's the first time I've ever had to buy one separately like this.

I was surprised to find such an odd thread size on such a common item.

I did realize later I don't need a castle nut - when I came here with my question I had just removed the old one, so was assuming that's what I need for the new one as well. It is not.

Thread size help

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