Front casting bolt size

TOH · Post by **TOH** » Wed Sep 30, 2009 5:34 pm

Hello. This is my first post to the new forum. I was a member of the old forum but I've been away for some time. My restoration project of the 1955 FMD has been on hold for a while and now I'm getting back to it. I got the tractor in autumn 2000 and started it in 2001 so the project has been a long one. I still need to sort out the 3-point lift parts and some other details.

Now that I finally got the mudguards intalled I'm looking forward to giving it a real test drive on the road for the first time and to do that I'll need to attach the registration plate. I'm going to use the holes on the front casting (around the starting handle) for that.

My question is what size are the holes? According to my measurements I'm quessing that they could be UNC 11/16". Is that correct? The problem is that I haven't seen that size for sale anywhere so I'm not sure if that size even exists. Only sizes available near that are 5/8" and 3/4" (= 10/16" and 12/16") and they don't fit. I would appreaciate a confirmation of the size so I can start asking around.

Best regards,

Timo

Post by **Brian** » Wed Sep 30, 2009 6:29 pm

Hi Timo,
Welcome back. You are correct about the hole size, a bit big for a number plate.

We used to drill and tap a 3/16th (approx 5mm) between them and bolt the plate on there.

TOH · Post by **TOH** » Wed Sep 30, 2009 6:49 pm

Brian wrote:Hi Timo,
Welcome back. You are correct about the hole size, a bit big for a number plate.

We used to drill and tap a 3/16th (approx 5mm) between them and bolt the plate on there.

Thanks for the confirmation. Yes, the bolts are a little big but I was thinking of making a bracket for the number plate so I won't need to drill such a big holes to the plate itself. If it wasn't the crank handle in the middle the front casting would be a perfect place for the plate. Now it has to be mounted either below or above the handle. I was thinking putting it above. The drill and tap approach is also a good idea. I'll consider that too.

Timo

henk · Post by **henk** » Wed Sep 30, 2009 8:21 pm

Hello Timo,

All UNC and UNF bolds and nuts are availeble at your NH dealer. I think they are cheap. Just ask around.

Kim · Post by **Kim** » Thu Oct 01, 2009 1:29 am

Henk is correct. I checked my NH dealer this evening and he has 11/16" bolts in several lengths.

Dandy Dave · Post by **Dandy Dave** » Thu Oct 01, 2009 12:43 pm

Kim wrote:Henk is correct. I checked my NH dealer this evening and he has 11/16" bolts in several lengths.

9/16ths is another size you don't often see. But it does exsist. I know for a fact that the size is used on a Model "AAA" Ford Duel wheeled 1 1/2 ton truck to hold the differential to the housing. I've also come upon it several other places in my long and wide range of repairs on equipment. Dandy Dave!

TOH · Post by **TOH** » Thu Oct 01, 2009 6:47 pm

Today I asked from a couple of places including a NH dealer but they didn't have them. My dad was a bit luckier. He asked from a small machining shop and the owned promised to order the bolts. The imperial sizes are a bit hard to get here in Finland.

Timo

TOH · Post by **TOH** » Thu Nov 05, 2009 12:03 am

Still no luck finding the 11/16" bolts but the guy who promised to order some for me, gave me an M18 (18 mm metric) bolt to try. Lo and behold, it fits perfectly!

There are two possible explanations. Either the M18 and 11/16" UNC are by coincidence almost identical in size or someone has forced an M18 in in the past reforming the threads. Or both.

I tried to find the size data for the 11/16" UNC bolts in the internet but I couldn't find any. I was going to compare the dimensions given for the two types to see how well they match. Does anyone have both of these bolts in hand so that you can take some measurements and compare the threads side by side to see if they are indeed similar? I would appreciate the help.

I would like to get to the bottom of this just to show the guy who gave me the bolts that it is indeed imperial bolts that fit there originally. He said that the holes are probably made afterwards but I know that it is not true. It also appears that he doesn't really believe that the 11/16" bolt size even exists.

Timo

Mike Kuscher · Post by **Mike Kuscher** » Thu Nov 05, 2009 1:30 am

Hi Timo,

Here is your information.

M18 is...
18mm Diameter (0.7087")
Core Diameter = 14.9328mm (0.5879")
Included Angle = 60 degrees
Pitch = 1.5336mm (0.0604") or 16.5 threads per inch

11/16" NC is...
0.6875" Diameter (17.4625mm)
Core Diameter = 0.5783" (14.6888mm)
Included Angle = 60 degrees

However, 11/16" NC was never a 'standard' size, it was always a 'special' or secondary class of thread. UNC threads go up in 1/16" from 1/4" to 9/16", they should then go up in 1/8" only from 5/8" onwards.

The thread angles are the same, the M18 diameters are slightly larger but may well fit due to the holes becoming larger through corrosion.
Here is the interesting bit though.
5/8" UNC standard thread was 11 threads per inch.
3/4" UNC standard thread was 10 threads per inch.
But 11/16" NC, because it was a secondary thread, could be obtained as two different pitches...
12 threads per inch, ordered as 11/16" 12NC (no 'U' quoted).
16 threads per inch, ordered as 11/16" 16NC.
The 'U' was dropped from the description because it was a size not in the standard or 'Unified' table, it only kept the 'National Coarse' part of the name.

Obviously, good old Henry decided to use 11/16" 16NC (Only half a thread different over 1"), so M18 will fit so long as you do not go much deeper than 1" or 25mm, which is the point you will start to do damage.

Regards,
Mike

henk · Post by **henk** » Thu Nov 05, 2009 8:10 am

Hello Mike,

Perfect discription. However I think after allready a few turns it will damage. M18 has 1.5mm pitch. 16UN will give 1.58 mm pitch. So after 3 turns you will have 0.24 difference. Together with the slighter larger diameter. I wont fit at all.

jkilmer83 · Post by **jkilmer83** » Thu Nov 05, 2009 8:10 pm

wow I didn't realize how hard it is to get a bolt over the pond is. Here in the us any corner hardware store would have that bolt but you would be harder to find a 18mm. Do you guys have festener distributor that supplys bolts to factories??

TOH · Post by **TOH** » Sat Nov 07, 2009 10:51 pm

Mike, that's awesome! Thanks very much for the info.

Something doesn't add up, however. The 18 mm bolts that I've got have 11 threads per inch (if I did the measurement correctly). Or now that I think about it, it may be more like 11.5 tpi. That is almost the same than the 11/16" 12NC. Maybe the 16.5 tpi is the fine threaded version of the M18? Should it be 11/16" 16NF instead of NC, bytheway? Just like UNF?

Anyway, as you said, I was able to screw the bolt in for an inch or so before it started to stick. I shortened them to slightly less than that and now they fit perfectly.

jkilmer83, metric bolts are the standard here nowadays (in Finland). The imperial sizes are not that often needed but they are available actually quite easily. It is the odd sizes, like the 11/16" that can be difficult to find. I'm sure those too are available from somewhere but I didn't manage to find them myself. Perhaps because I asked for "UNC" when I should've asked "NC" as Mike pointed out.

Timo

JC · Post by JC » Sat Nov 07, 2009 11:20 pm

I'm not sure about getting an 11/16 NC bolt at the corner hardware store. I've been operating and repairing farm and heavy equipment all my life, and I never knew that size existed until I read this thread. The 18mm x 1.50 bolt is available at most car and truck parts stores here.

TOH · Post by **TOH** » Fri Dec 18, 2009 10:44 pm

Here is a picture of the finished license plate bracket (backside). It is already installed but I can't get a picture of it now. I would need to move the tractor for that but it won't start until it gets a bit warmer. It has summer diesel in the tank and for a few days it's been under -20 degrees celsius. Today was a bit warmer, only -10. The fuel is probably frosen solid. I tried to start her the other day to no avail. Starting at those temperatures is probably a bad idea anyway...

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