[Womble]

Hi folks, this is a long shot, but you never know what folks on here will know!

I'm looking for a castle nut for a USA-made lawnmower axle. The manual says it's a "Hex Castle Nut, 3/4-28 UNEF"....... but I can't find one anywhere, and am starting to doubt that such a thing even exists.

My understanding is that the 28 is threads per inch. However, I just can't seem to find one, and when I look up the charts here and here, 3/4" UNEF seems to correspond only to 20 threads per inch.

Can anybody put me out of my misery!?

[doganjo]

Can anybody put me out of my misery!?

I'll come over with my loaded pink starting pistol.  That will shock you into coming out of your misery 

Sorry, I'm not a mechanic or scientist so can only be facetious 

[chrismahon]

I hadn't heard of UNEF(extra fine) until you mentioned it [member=2128]Womble[/member] . My Zeus charts only list UNC (coarse) and UNF (fine). My thought is that either the ¾ or the 28 is wrong, so it's ½ or 20. The only way you are going to find out is to measure the bolt/ male thread. So the major diameter is 0.75" or 0.5" (19.05 or 12.7 mm) and as you thought, the number of threads per inch is 20 or 28.

[Womble]

Thanks Chris, I'll get the calipers out and count the threads.

I did Email a Scag dealer to get a quote for the official part, but check this out  ....

[chrismahon]

That's quite a price Womble, for something that perhaps costs 50p to make. Of course everyone in the supply chain is taking a markup. I remember someone I worked with telling me that he worked in Australia for a while at a brake cylinder manufacturer. One particular cylinder left the factory at $2.30 and as a spare part was being sold for $75.00.

[Womble]

OK, I got my ruler out. They're definitely 3/4" x 20 TPI, and those are available far cheaper elsewhere.

I dread to think of the bill when something goes properly wrong with it though!