Filler cap thread size???

bullseyex · Oct 10, 2011

Hello All,

I just have a quick question. Does anyone know the thread type of the red hydraulic filler cap on a Kubota L3400HST?

I know that is 1" and I know that a O-Ring SAE 16 will not fit. It will only thread on 1/2 turn. I am hoping that a 1" NPTF is the one I am looking for. My Kubota is a 50 miles away at a camp and I would like to take the appropriate fitting with when I head out there.

I want to finish up on my rear remote project and running the tank return to
a fitting where the filler cap is is a nice short run from the 3 spool valve.

I would be very greatfull for any input and will post pictures when project is complete.

This is a great site with a lot a very helpful people.:thumbsup:

See pic below ( I hope this works, I have not done this before)

KawiBoy450r · Sep 19, 2025

bullseyex said:
Hello All,

I just have a quick question. Does anyone know the thread type of the red hydraulic filler cap on a Kubota L3400HST?

I know that is 1" and I know that a O-Ring SAE 16 will not fit. It will only thread on 1/2 turn. I am hoping that a 1" NPTF is the one I am looking for. My Kubota is a 50 miles away at a camp and I would like to take the appropriate fitting with when I head out there.

I want to finish up on my rear remote project and running the tank return to
a fitting where the filler cap is is a nice short run from the 3 spool valve.
Loop
I would be very greatfull for any input and will post pictures when project is complete.

This is a great site with a lot a very helpful people.

See pic below ( I hope this works, I have not done this before)

Been a while I know but did you ever figure out what size these threads are? To me they are an od size and pitch. I’m in a similar project wanting to run a return to a full cap on a Kubota.