Oddball Thread Designation

M24 looks to be a European/Australian metric standard.

TF looks to be this:

TF represents fully tensioned, friction type joint

48/57 may have something to do with galvanizing thickness

Maybe more clues here:

http://www.gaa.com.au/index.php?page=bolting

M24 bolt 48 long 57º pitch threads fine....just guessing

I don't know anything about this sort of thing but I'd guess the first bit is M24 between 48 and 57 mm long. The position where it's fitted maybe constrains it to be between these two lengths.

My guess and it is only that is: 24 mm dia full thread 48mm min to 57mm max. It doesn't sound like any standard callout. Sometimes people will put down what they think is a good description, but is not familar with standard callouts on drawings.

Here's a guess:

This is an exortic spec, M24 (guess X3) Thread stripping area (sq. mm/mm engagement) external - 48, internal - 57. tf = transition fit.

If correct, some spec. writer is getting a little frisky here.

48/57 tensile force? ( but what units? )

The numbers are sq.mm/mm engagement. Yes, tensile stress area.

Standard for an M24 X 3 is 40.5 external and 55.0 for internal.

I am getting this information out of a publication called "IPT's Industrial Fasteners Handbook." Personally, I am not expert in this subject but have had fastener problems in the past and hence the acquisition of this handbook.

Hi Baffled,

I've read this book too. "IPT's Industrial Fasteners Handbook" is really exhaustive in this field, in addition is a very convenient tool useful for engineers, draftsmen and supervisors..in the sector of aerospace, fabrication, repair as well as shipyard.

...thread designation...M24-48/57tf...

Where did you encounter this designation?

All i can think of is the left "V" gear train on a lathe for metric thread cutting is 48/57. Couldn't tell you what "tf" is.

Sounds like a Tap, TF= thread forming

M24 tap would require a hole around 48/57 of an inch. Oddball I know but 48/57 of an inch is 21.4mm and thats about right.

http://www.kasthurimmc.com/tap-drill-chart.html

Different charts will give you different hole sizes

Still guessing though

Are you able to put this thread in a context that may narrow down the possibilities or jog one of our memories?

Where is the thread being used and what part is threaded?

That designation belongs to a drawing and is rather specific for that size and thread.

It is NOT a bolt description, although not a regular Metric M24 one.

My guess is that a hole has to be drilled and tapped with a depth of minimal 48 mm and maximal 57 mm -

If you get your designation from a French drawing tf means 'tout fond'. (up to the bottom) - a so called blind hole.

But again, more info needs to come from you.

Dohhhhh 24x2=48mm. 2 bolt diameters thread engagement. Makes perfect sense.

2 nut lengths on a studbolt and the same length on a puller sleeve for bolt tensioning.

Though neither are blind. Still makes sense though, with you on that one.

More info from the OP needed, where do these guys go after posting? Reminds me of ringing doorbells and running away as a kid.

Thank F*&# we now know what TF stands for. Wouldn't it be nice if every drawing or spec that you came across had a Key/Legend attached. I guess some people just like to make themselves feel important ;)

Nice thread.