Help determine prop nut size

[zzptichka]

Looks like 7/8" but TPI is somewhere between standard 9 and 14. Looks like a 12?

This is an older Gulf 40 boat. Shaft is 1-1/4". So the nut could be of some British standard.

Thanks in advance!

[MicHughV]

You should be able to get a thread gauge at most hardware stores...

[SailingHarmonie]

Originally Posted by zzptichka

Looks like 7/8" but TPI is somewhere between standard 9 and 14. Looks like a 12?

This is an older Gulf 40 boat. Shaft is 1-1/4". So the nut could be of some British standard.

Thanks in advance!

This is NOT a bolt, with bolt standard threads. 7/8” prop nuts have 11 TPI. Without a proper caliper measurement it’s hard to be sure but looks a match.

[zzptichka]

Originally Posted by SailingHarmonie

This is NOT a bolt, with bolt standard threads. 7/8” prop nuts have 11 TPI. Without a proper caliper measurement it’s hard to be sure but looks a match.

If I'm not mistaken, 11 TPI (on 5/8" nut) is standard for 7/8" shafts. This is 1-1/4" shaft that needs a 7/8" nut.

Working on getting the gauge. Where we are right now there are not a lot of hardware stores.

[deblen]

Suggest you measure the OD of the shaft on the non-tapered portion & then consult a table.
Most shafts comply with "table" nut pitch & size.
Cheers/Len


https://propshopinc.com/the-prop-blo...-marine-shaft/
https://www.generalpropeller.com/Pro...Shaft-Nut-Kits
SAE & METRIC Chart. https://www.propellerpages.com/?c=ar...-04_Taper_Bore

[zzptichka]

Originally Posted by deblen

Suggest you measure the OD of the shaft on the non-tapered portion & then consult a table.
Most shafts comply with "table" nut pitch & size.
Cheers/Len


https://propshopinc.com/the-prop-blo...-marine-shaft/
https://www.generalpropeller.com/Pro...Shaft-Nut-Kits

Yep, this table is for SAE J755 standard and this shaft most definitely was manufactured before this standard was adopted in 1980.

[deblen]

https://www.amazon.com/Digital-Calip...s%2C197&sr=8-4





https://www.amazon.com/ChgImposs-Imp...s%2C189&sr=8-3

[wholybee]

I suggest you take it to a prop/shaft shop. I just had to do this with my shaft. Mine was an inch 1-1/4 shaft, with the correct 7/8-9 threads, but the 7/8-9 threads with my new max-prop did not fit.

Apparently the tolerances are not followed well, and the diameter of my threads a bit to large, even though it nominally was 7/8". The machinist said that it was very common and they need to resize threads all the time.

Your picture does look like 12 tpi. You could also have some oddball shaft. Maybe at some point someone had a specific propellor they wanted to use, and just resized the taper and threads instead of changing the shaft or buying a new propellor.