M12 screw thread - 'TD' versus 'S'

[SimonFisher]

I bought some M12 A2 stainless steel bolts to use with lengths of studding that I already had. The thread on the studding is (standard?) M12 x 1.75, I know this as I've been using a die to clean up the thread after cutting to length with a grinding disc.

Most of the bolts are compatible with the studding and are stamped 'TD'. A handful however appear to have a thread of different pitch or other characteristic. They're stamped 'S'. Can anyone tell me the meaning of 'TD' and 'S'?

[Wendelspanswick]

If you mean the bolts are stamped with an S (or do you mean hex nuts) then they are imperial and not compatible with the metric studding.
Imperial fixings (Whitworth, BSF, UNC, UNF) used to use a letter for the strength rating (o, r, s, t) while metric fixings use a number (8.8, 10.9, 12.9 etc). Just to confuse matters modern manufacturing runs of Imperial fixings can also use numbers or letters for the strength codes.
The TD is likely to be just a manufacturers initials, never come across it as a identity code before.

[Wendelspanswick]

Have you tried laying the studding against the threaded portion of the bolts, you should get a perfect match with no gaps. If the threads mesh at one end but go out of sync further down you know you have different thread forms.

[Wendelspanswick]

Oh and I would advise you not to Google "S TD On Nuts" unless you want to be put off you breakfast.

[SimonFisher]

If you mean the bolts are stamped with an S (or do you mean hex nuts) then they are imperial...

Sorry, my mistake, I meant that some of the hex nuts are stamped 'S'. I've emailed the supplier as he appears to have supplied me a mix! In an order for 60 M12 hex nuts, I've got 15 marked 'S', which I now know means they're imperial, thank you. I was cutting some of the studding to length yesterday and happened to have picked up a couple of the imperial nuts to make sure the thread on the cut ends were clean. I thought I was having a particularly bad day as they obviously wouldn't fit!!!

[oldclaypaws]

A crucial bolt (securing the drive shaft) dropped off the bottom of my tractor shortly after purchase and a search ensued for a replacement. Fortunately I went to the right place, a specialist tractor spares supplier, Denleys. I had the right thread but needed a longer bolt. With various gauges it took the guy about 3 or 4 minutes to work out it was a UNF, an American thread. It took 3 phones calls to find a supplier with the right thread and length. I'd always thought there were 2 threads, Metric and Imperial, but he explained there are SIXTEEN. Then there's the different pitches, what a nightmare ! There are multiple manufacturers stamping initials on them just to confuse matters. Your TD is maybe a makers stamp.

It the position it was, is should have sensibly been a left hand thread, but it wasn't, meaning it could easily come out again. To be sure it didn't as getting all the belts on correctly was tricky, I put a generous layer of bolt lock on it, and a spring washer.

Life was so much simpler when Dr Frankenstein fitted the bolts in my neck keeping my head on. They're getting rusty now and could do with replacing, but its the usual problem, I'm now obsolete and you just can't get the parts.

[Wendelspanswick]

Next time you need a bolt OCP try Wentins Fastenings in Yeovil, its a sort of supermarket for bolts with shelves and shelves each stacked with labelled boxes of nuts and bolts in various materials, sizes, thread forms etc.
You can self serve if you want and buy 1 or 100, excellent prices and very knowledgeable staff.
They are on the Pen Mill estate.

[Binz]

**** Moderator edited to correct quoting ****

I've been using a die to clean up the thread after cutting to length with a grinding disc.

alternatively, put a nut on before cutting, then just undo the nut and it straightens out any burs

[SimonFisher]

I've been using a die to clean up the thread after cutting to length with a grinding disc.

alternatively, put a nut on before cutting, then just undo the nut and it straightens out any burs

I've done that before if cutting bolts down with a hacksaw. Cutting 12mm thick stainless steel off 3 metre long lengths is quicker with a grinding disc but seems to leave the end in a worse state and I wasn't sure if the trick with the nut would work as well. If the nut and the bolt are the same material and same hardness, isn't there a risk of the burr damaging the thread in the nut?