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Confusing t-slot dimensions

I have 4 t-slots on three machines, none of which I can find a nut size to match

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Kevin Cobley20/02/2021 21:42:46
17 forum posts

Being relatively new to machining, I'm starting to worry that I'm on the wrong track with finding t-nuts for my various machines. I thought this might be simple

I have 4 machines with t-slots and none of them seem to have standard metric sized nuts. Even imperial sizes I can find on the web dont seem to match.

What have I missed?

The machines and their slot measurements:

measuremnts s1 is the slot width at the top of the opening, a1 is the slot height that the head of the nut goes into, t1 is the width of the slot at the bottom, h1 is the total depth of the slot.

Boxford Model C topslide :

s1=8.6mm, t1=17.5mm, a1=12.6mm,h1=12.62mm

This is an imperial machine so more likely an imperial size.

Hauser Mill Table slots

s1=7.85mm , t1=15.1mm ,a1=4.68mm , h1=9.37mm

Hauser Mill slideway stop slots:

s1=5.8mm , t1=13.1mm , a1=5.00 , h1=9.66mm

Being Swiss, I'd expect it to be metric as everything else on this machine is.

Bandsaw table:

s1=9.0mm t1=14.3mm a1=5.5mm h1=8.7mm

European build metric bandsaw.

none of these match the standard sizes here:

Thanks for any insight..

Saxalby20/02/2021 22:19:40
173 forum posts
23 photos

My lathe, mill, shaper etc etc all have different t-slots. Like yourself I despaired at trying to find the right sizes. So made my own for each machine and just bought the standard 5, 8 and 10mm studs and nuts.

Regards Barry

Kevin Cobley20/02/2021 22:28:18
17 forum posts

I see a chicken and egg problem - not having any way to hold stock on the mill to mill the t-nut

Saxalby20/02/2021 22:35:26
173 forum posts
23 photos

I must admit I did buy a couple of t-nuts that sort of fitted the mill to get started.


Kevin Cobley20/02/2021 22:40:38
17 forum posts

I'll have to get the files out then Seems odd that it should come to that for such a simple thing!

Zan20/02/2021 23:51:32
282 forum posts
19 photos

You got a machine, so mill t slot nuts to suit each one Using nuts in place of proper t nuts will give you grief in the long term. Make them, it would take less time than typing your post.....

all my 4 millers which I have had had different sizes. First task with each new machine was to mill sone new ones...

Edited By Zan on 20/02/2021 23:55:21

Zan20/02/2021 23:53:31
282 forum posts
19 photos

Ps you need good clearance with t nuts, so decimal mm dimensions for them come with the fairies

not done it yet21/02/2021 08:41:35
6350 forum posts
20 photos

A couple of coach head bolts may well suffice to get started. Obviously not ideal, but can soon be replaced with the first items made for the job. Just need to think ‘outside the box’ a bit.

Journeyman21/02/2021 09:08:27
1035 forum posts
200 photos

You can make T-nuts using the lathe, saves a lot of filing compared to normal rectangular ones!


More detail ** HERE ** if required.


Nicholas Farr21/02/2021 09:09:56
3001 forum posts
1371 photos

Hi Kevin, you can knock off about 1mm of your t1 measurements and about 3mm off the height at the bottom of your h1 measurements, these need to be a good clearance and your s1 measurements will need a easy fit, so you could knock off 0.2mm of these measurements. You can make T nuts on your lathe like the one below from a piece of square or rectangular bar or even a larger piece of round bar and then cut two flats on the bottom to suite your slots. It is also a good idea to make your a1 measurement a little less, say about 0.3mm, so that they are below the surface of your table.

t nut 1.jpg

You could also use a suitable piece of flat bar and drill and tap a hole for a piece of threaded rod.

t nut 2.jpg

A few of these will get you going to be able to hold things, to make the more conventional T nuts to suite your purposes.

Regards Nick.

Edited By Nicholas Farr on 21/02/2021 09:26:24

Nigel McBurney 121/02/2021 09:16:51
926 forum posts
3 photos

Be careful using modified bolts etc instead of tee nuts,I have seen in my travels lumps taken out of Tee slots by using the "wrong " nuts, or even just overtightening ,rotary tables seem to suffer more than mill tables. I never really understood why manufacturers did not get together and come up with a standard series of T slots. And its not only mills,rotary tables,shapers,vertical slides, cross slides, lathe steady t slots (older Colchesters),drilling m/c tables and on and on ,they invariably have variations in tee slot dimensions ,then the commercial T nuts used BSF ,Whitworth,and unified threads plus newer nuts use various sizes of metric threads.The most annoying machine I have is the table on my one inch capacity Meddings pillar drill,it has two tee slots running back to front to back, The full depth of the tee slot is cast and it tapers,so a T nut is slack at one end and gets tighter towards the other end,and invariably jams on a bit of swarf. Should have taken the table off years ago,and machined the slot but was too busy getting a living and now I just live with it ,with a larger capacity drilling m/c I usually bolt down the work or vice when using drills over 1/2 inch, A m/c with 1 hp motor and high torque with belt and gear reduction does not slip.

Nicholas Wheeler 121/02/2021 09:44:42
746 forum posts
52 photos
Posted by Journeyman on 21/02/2021 09:08:27:

You can make T-nuts using the lathe, saves a lot of filing compared to normal rectangular ones!


More detail ** HERE ** if required.

Also true if you have a small milling machine; power feeds and larger cuts save a lot of boring work. It's also a good way of using up stubs of material that are unlikely to be of any other use.

Kevin Cobley21/02/2021 10:21:26
17 forum posts

many thanks for the responses. Glad to see I'm not going mad and that I need to make my own. Particular thanks for the for the clearance information. I assume you need a bit of clearance around the head to allow for swarf not jamming the head, hence the suggested dimensions.

I'm aware that on all my machines that the tslot aspect ratio is shallow. The mill is a small one (I'm more interested in watches and clocks than cars and steam engines) so being gentle with the slots is a must - also the mill table is pristine, so chipping a slot would be heart-breaking.

The threaded rod in flat stock might get me going on the mill as I can make the bar long enough to spread the load.

Looks like I have another project

Clive Foster21/02/2021 10:46:01
2838 forum posts
103 photos


When making T nuts I prefer light alloy rather than steel. Sufficiently strong and if a bit of swarf gets in the way it will be ground into the nut rather than the underside of the Tee slot. Much easier to dig out!


Nicholas Farr21/02/2021 10:55:40
3001 forum posts
1371 photos

Hi Kevin, don't go overboard with the length of any T nuts, the threaded flat bar ratio of the length / diameter of the threaded rod is about right, but you must get the hole drilled and tapped as square to the top of the bar as reasonable as possible. I should have said that the thickness of the flat bar one is only about 0.5mm shallower than the slot, in order to get the maximum amount of threads tapped into it and I also staked the bottom of the threads with a dot punch, to stop the threaded rod screwing through and acting like a jack on the bottom of the slot, as it is something you really don't want to happen. Most commercially made T nuts are either staked in a similar fashion or the threads a left a little tapered in the bottom of the hole, or even not tapped completely through.

t nut 3.jpg

Regards Nick.

Georgineer21/02/2021 11:29:06
524 forum posts
31 photos
Posted by Nicholas Farr on 21/02/2021 10:55:40:

... I also staked the bottom of the threads with a dot punch, to stop the threaded rod screwing through and acting like a jack on the bottom of the slot, as it is something you really don't want to happen...

Absolutely! A previous owner has done this to the cross-slide on my ML7, and the edges of the T-slot are broken out.

George B.

Perko721/02/2021 11:37:26
394 forum posts
31 photos

I've successfully made odd-sized T-nuts for an old Ideal lathe and for a new vertical slide, all from 12mm square MS bar, using a bandsaw and files to get the right shape and dimensions and the usual drill and tap for the threaded hole. Took a little while with plenty of perspiration as well but did wonders for my filing technique!

Howard Lewis21/02/2021 11:46:08
5348 forum posts
13 photos

You only need to do things the hard way twice.

Make two Tee nuts, with as little effort as possible, to secure the vice to the table of one machine. Then first job is to make two "proper" nuts for thet machine, and fit them.

After than you can produce Tee nuts for any other machine, as and when the need arises.

To make aligning the vice(s ) as easy as possible, my suggestion would be to make a "goalpost" fixture for each machine and vice. The only precision bit is to turn the "dowel" at the bottom end of each post.

There may be a picture in my album. But If I go to check, I shall lose this. Hopefully the Forum upgrade will remove that danger.


Howard Lewis21/02/2021 11:53:03
5348 forum posts
13 photos

Second Image All we need to do is to enlarge it! All that I seem to do is to call up the image and a whole load of Latin!

881331.jpg HTH



Linked the full-size picture. Dave

Edited By SillyOldDuffer on 21/02/2021 12:19:03

John Haine21/02/2021 11:54:41
4189 forum posts
242 photos
Posted by Howard Lewis on 21/02/2021 11:46:08:

There may be a picture in my album. But If I go to check, I shall lose this. Hopefully the Forum upgrade will remove that danger.


Just open another window, use that to check your album, you'll be logged in already. Then come back to the first window to add the picture.

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