Clamp Sets - Thread Type?

I have two of the common commercial machine-tool clamp-sets, bought a long time ago, separately from different stockists - I forget whom and when.

The threads seem the same on both sets, and are definitely 3/8-inch X 16 tpi... but UNC or BSW?

Same pitch, different flank angle; slightly loose fits and I cannot gauge them accurately enough. A Whitworth screw fits the nuts, but whether correctly is another matter.

(A mismatch would give a line rather than surface contact, risking undue strains, distortion and wear.)

Since I wish occasionally to make additional jigs, T-nuts for other tables, etc., compatible with the purchased fittings, I would like to use the proper threads.

So does anyone know for certain, please?

Since M10 x1.5 is a pitch of 16.9 TPI it would be easy to make a mistake with 3/8 x16. I would go with BSW though the difference (unc) is so small I would not worry about it ! Good Luck, Noel.

The spanner size for the nuts should be a giveaway.

3/8" BSW 18.03mm 0.710"
3/8" UNC 14.29 mm 9/16"

(M10 would be a 17mm spanner)

Bill

As the US market for many of the imported items is far greater than the UK my bet is on UNC.

EDIT, had a look in the MSC catalogue and they list all the imperial sized ones as UNC, both cheaper Interstate brand as well as better Gibraltar sets and separate studs and nuts.

Edited By JasonB on 08/11/2021 07:24:18

Invest some of the grandchildren's inheritance into a 1/2" set and then there would be no doubt.

Photograph them, enlarge and draw over the photo on the computer.

The spanner size for the flange nuts used on clamping sets is not always standard: I have M12 with 22mm A/F and M14 with 22mm A/F (which is good as my drawbar is also 22mm A/F and other bolts on the machine are 7/8" A/F, so one spanner fits all).

Have you tried a (good) UNC nut, to compare the fit?

Have you studied the thread form at the peaks and troughs?

I note (most?) 1/2” sets on offer are 1/2’ - 13? (I might look further at those).

Edited By not done it yet on 08/11/2021 08:46:52

I have metric pitch, Whitworth and UNC thread gauges. I checked my kit before ordering some 12" x 1/2" UNC studs.

Martin C

For all practical purposes on your clamping sets UNC & BSW will be totally interchangeable, most are made so poorly it is impossible to tell what they are meant to be, but from memory I do remember UNC was prevalent.

Tony

Hmm - spanner size. I just bought a set for my Novamill, the studs are M8 but the flange nuts are 17mm a/f! The strap clamps have wide slots so they can be used across different stud sizes.

Thank you chaps!

Peak4 - A/F and Whit. spanners don't fit them! They take 17mm spanners even though not M10 threads.

NDIT - I thought of that but unfortunately found only I have no sample UNC nuts. Nor could I examine the thread forms fully enough. Howeve the 1/2" - 13 you quote is UNC, differing from BSW (12tpi) and BSF (16tpi). I keep a Tracy Tools poster-size chart by my computer for good reasons!

Martin - I did try thread gauges but could not obtain a convincing match with any of them.

So, overall, it does look as if UNC is the more likely, and the easier to obtain.

Very often, using a set-screw or bolt is better than the stud, especially where the height is restricted.

'

Spanner sizes, I am afraid, are no guide to sizing flanged nuts, both on these clamp sets and those bought as general fasteners. The nuts on my clamp sets take a 17mm A/F spanner, standard for ISO-M10 Coarse, but the nuts are certainly not M10. (An M10 bolt will not even enter the thread.)

My club's portable track fishplates have M10 or M12 flanged nuts readily available from builders' stockists; but the forged, heavily-tapered hexagons are not those established for their standard M-n Coarse thread, Fortunately the spanner they accept is readily available, just not the normal one. I found this too with some of the building-trade fastening holding the overhead-hoist columns to my workshops' concrete walls, and I think their nearest spanner was a Whitworth despite the fasteners being otherwise metric!

I have what i thought was a Whitworth tap and die set that I picked up secondhand decades ago. They half inch is marked Whitworth, but the rest are dia and tpi. Makes me wonder if it was sold as UNC or Whit with the half inch only determining what it was sold as. Will look more closely at the thread profile.

The two mills at the museum use different sizes, the drill mill uses 1/2 UNC but the Tom Senior is smaller. I got a set of 3/8" but soon changed the studs to metric 10mm and put 10mm helicoils in the nuts. 10mm studding is easy to get hold of and can be any required length. The rest of the set was ok, except that we made some 10mm tee nuts that fit much better in the tee slots.

If a 17mm spanner fits them then 11/16" AF will fit them too.

.

Flank drive, I trust …

MichaelG.

Generally Whit nuts go onto UNC bolts but not visa versa. Of course it depends on the quality of the items and how much slop was built in using production machinery well past its use by date.

As stated earlier these sets if you are talking about the typical ones in a red sheet metal holder are always made for the American market so UNC. You then find individual T-bolts in an estate sale >50 years old probably which are Whitworth.

Well, they are free-running nuts on their studs, so these might work "vice versa"!

I've ordered a batch of UNC nuts and bolts to add to the collection, for the applications where the standard clamps are a right bloomin' nuisance. (E.g. holding a vice whose slots run under other parts of the appliance).

I've also a collection of UNC/F taps and dies so making extra studs now and then won't be a problem, though UNC studding is probably reasonably easy to obtain.

The one that does not swap is 1/2" whit is 12tpi, unc is 13tpi. Noel.

You can exert a large clamping force with quite a small thread.

You can crack a casting with 1/4 BSF commercial studding!

A 1/2 x 20 tpi UNF bolt in W range steel will take an axial load of 9 tons to put into yield.

So a 1/4 BSF, 1/4 UNF or M6 should be able to provide a clamping force of over 1 ton, even with mediocre material..

Howard

Imperial machine slots use imperial T nuts, BSW or UNC, metric machine slots use metric threads. Nuts can vary in AF size wether they are collar nuts or plain full nuts. WDS is useful to see the actual sizes.