Looking thru my seventh edition of the machinist handbook, copyright 1940.
The only 27 pitch threads I could find were 1/16 and 1/8 tapered pipe and straight pipe threads.

Tapered.
https://www.engineeringtoolbox.com/npt-national-pipe-taper-threads-d_750.html
Straight pipe.
https://www.engineeringtoolbox.com/american-standard-straight-pipe-threads-d_1520.html

If you have a machinist friend that knows his salt, check with him.
Don

1967 GMC 9500 Fire Ladder Truck
"The Flag Pole"
In the Stovebolt Gallery
1946 2-Ton grain truck
1946 3/4-ton pickup,
1953 1-ton pickup
1957 1-ton flatbed dually,
1954 Pontiac Straight Eight
Of all the things I've lost in my life, I miss my mind the most!