Heads up for 7/8-18 tap source

Tom Fleming · Jan 21, 2012

Have been looking for a 7/8-18" tap for awhile now to have in the shop to chase threads on engines using the old style spark plugs. I had sticker shock on most of what I found.

Then I stumbled onto this on ebay. Ordered one. VERY pleased. IF any of you are looking to have a decent tap on hand to chase spark plug threads on the older engines, here's the link:

http://www.ebay.com/itm/250960577421?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Captndan · Jan 21, 2012

I have a reversible one for both size threads. It was about
$10.00 at the auto parts store.

Tom Fleming · Jan 21, 2012

Dan, I bought one of those and don't know if I got a bad one or what, but I found that the thread profile didn't quite match what was in the heads, and always was shaving metal off and got "loose" thread results.

So, I decided to go with a dedicated machine tap for the job. Like I said, I might have got a bad one, but I was not pleased with the performance of the one from the autoparts. Goes with the old cliche, "your mileage may vary......" :wink:

mike1972chev · Jan 21, 2012

Tom,You got me curious???

What is the letter designation AFTER the 7/8-18 number??? (example: NC NF NTPT ect????)

Tom Fleming · Jan 21, 2012

NS

Kevin B from Illinois · Jan 21, 2012

NC Course thread, NF fine, and the last one is pipe thread.

Tom Fleming · Jan 21, 2012

Kevin, NPT was what I always thought pipe thread was, National Pipe Thread.

Not sure what NS is.........because this tap is definately NOT tapered.

randy hall · Jan 21, 2012

Tom. npt is national pipe tapered. nps is national pipe straight.

Tom Fleming · Jan 21, 2012

Randy, agreed, but what is NS?

teddy52food · Jan 21, 2012

NS may mean not standard.

randy hall · Jan 21, 2012

N S is unifed inch screw thread, special diameter or pitch, or lenght of engaagement.

willie in mn · Jan 21, 2012

You don't want a tap. A tap has cutting edges, removes material in use.
What you want is a chase. It has rounded edges, gently pushes threads back into proper position without removing anything.
Have a double ended chase on hand, cost less than 10 bucks. Works on everything I have here, Briggs, Tecumseh, Chev, Kohler, Allis Chalmers.
Willie

mike1972chev · Jan 21, 2012

What does the "NS HSG" suffix stand for on this tap Tom?

billde · Jan 21, 2012

NS means it conforms to 60 deg thread, special as in not standard pitch for the diameter. Also notice this is a bottom tap, not the best for chasing threads as there is no lead to catch the old thread.

Tom Fleming · Jan 21, 2012

Here is a close up of the tap end. Looks like there is a short lead in on this one. I am by no means a machinist, but have worked with a few. Bottom taps that I have used (I don't own any) had zero lead in. I was taught to tap the blind hole with a regular tap, then finish off with the bottom tap. Like I said, I am no expert or machinist.

Dave_Id · Jan 21, 2012

NS is National Special

billde · Jan 21, 2012

1 to 2 thread lead is considered a bottom tap, 4 to six for plug, 8 to 10 for taper.

Tom Fleming · Jan 21, 2012

Bill, thanks for the info. I learn something on here almost daily. I appreciate it.

Dave S. · Jan 29, 2012

Tom have you tried the tap on a head yet and how did it work

Tom Fleming · Feb 2, 2012

Dave, yes I did and it works great! Threads seem to match very nicely. I am pleased with the purchase.

Heads up for 7/8-18 tap source

Well-known Member

Member

Well-known Member

Well-known Member

Well-known Member

Member

Well-known Member

Member

Well-known Member

Well-known Member

Member

Well-known Member

Well-known Member

Member

Well-known Member

Well-known Member

Member

Well-known Member

Member

Well-known Member

Similar threads