These nuts make me nervous, with just one thread on them. I have been tossing them away and reusing the old nuts with three threads on them. I keep telling myself that Fluidmaster would not be still supplying these nuts if they had a record of failure but I still do not use them.

There is a delicate balance in how tight these nuts have to be. Not tight enough and you can have the customer call you back six months later saying there is a leak under the tank. So the nut has to be quite tight and I just do not feel comfortable tightening a single thread nut that tight.

I know bernabeu has posted before about using FM fill valves with the brass shank.

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638



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Not sure where your getting your material or the model your getting

But the pro45 has a way better plastic nut supplied with the fill valve

i stand corrected

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

The single thread nut is supplied with the plastic shank models, like the basic 400A. IIRC even the 400ARHR comes with these nuts.

I use the Fluidmaster PRO45H and it comes with a beefier nut.

I have seen that thin nut and thought what bean counter come up with that thing.

I will use a thicker nut if available.

all that nut does is hold it in place.
its not like a faucet where someone turns a handle (sometimes too hard)

Hello.....

You need that more robust nut so that it takes longer for the rat to chew through it when he is looking for water.

Or that aggressive cleaning person keeps hitting the supply line etc. with her mop.

"all that nut does is hold it in place".

It does more than that, packy. It also seals against water leakage. If the rubber gasket is not sufficiently compressed at installation, you could end up with a callback because of water under the tank.