Couple of odd taps

R

reggie_obe

Diamond

Joined

Jul 11, 2004

Location

Reddington, N.J., U.S.A.

• Aug 3, 2021

• #1

Found in a box of mic. at an estate sale. Larger is marked 3/4-27 cutting length nearly 3", the smaller 3/8-27, slight taper to the teeth on both.
Marking appear hand stamped, no manufacturers name.
Are these UNS series? What was the application for a high pitch number in a 3/4" diameter?

 

fciron

Stainless

Joined

Oct 14, 2009

Location

Louisville, KY, USA

• Aug 3, 2021

• #2

Isn't 27tpi common in plumbing?

 

M

Milland

Diamond

Joined

Jul 6, 2006

Location

Hillsboro, New Hampshire

• Aug 3, 2021

• #3

fciron said:

Isn't 27tpi common in plumbing?

Click to expand...

I'm thinking more electrical in this case. Like threads on tubing for wire runs, then you need a mating thread in a housing or for a retaining nut. Like an old table lamp.

 

Rudd

Stainless

Joined

Jul 30, 2003

Location

savannah, jaw-ja

• Aug 3, 2021

• #4

1/8" National pipe is 27, it's about 3/8" OD. 1/4" is 18, about 1/2" OD

Edit, it may be electrical, but I work on quite a few lamps etc - and they tend to use NPT I've found one instance of metric, and it was an oddball metric thread, 14MM x 0.7.

 

G

Greg Menke

Diamond

Joined

Feb 22, 2004

Location

Baltimore, MD, USA

• Aug 3, 2021

• #5

I picked up a 3/4-20 NEF tap in a basement cleanout- used it to tap a hole in a motorcycle oil pan to take a bronze plug turned for a tight fit. The fine threads were helpful because of the fairly thin casting boss.

 

Conrad Hoffman

Diamond

Joined

May 10, 2009

Location

Canandaigua, NY, USA

• Aug 3, 2021

• #6

In my years making various lab, optical and scientific equipment, I've seen all manner of very fine threads on relatively large taps. 1/4-80, 1/2-40, 1/2-80, 1.032-32 and so on. Usually used for fine adjustments or, as said above, because wall thicknesses were limited.

 

1yesca

Stainless

Joined

Jun 1, 2004

• Aug 5, 2021

• #7

star machine works in san diego like to use 27 tpi on there stuff like the bullet punch on there lub sizer 1/2 x 27

 

S

Scottl

Diamond

Joined

Nov 3, 2013

Location

Eastern Massachusetts, USA

• Aug 5, 2021

• #8

If I recall correctly, 3/8-27 is the standard lamp nipple thread, which is a straight pipe thread.

3/4-27 also sounds familiar. I think I once measured internal threads in a brass lamp shade frame that matched that. Been a long time so memory is not that clear.

 

JST

Diamond

Joined

Jun 16, 2001

Location

St Louis

• Aug 5, 2021

• #9

IIRC the "brass" industry had 27 tpi for a lot of things.