TD2 bolt head diameter variations

[chadx]

So I was fiddling with the settings on a pair of TD2. As I looked closer, I noticed that the M6 bolt heads had two varied diameters. Both the M6x12mm and the M6x16mm bolts showed this variation within their length group (aka some 12mm had larger heads and some smaller. Some 16mm had larger heads and some smaller).

When using the M6x16mm to hold down the center disk, the one with the ever so slightly smaller head diameter seems to sink further into the recess. Also, with the M6x12mm holding the sole blocks to the base plates, the slightly smaller diameter head seems to fit in the positional grooves ever so slightly better.

It is so subtle, it seemed like my imagination, but it's there. The diameter of the larger heads measure 12mm and the smaller 11mm. That's only 1mm difference in diameter, but is noticeable in circumference as the bolts seats in the recess.

I pulled out all of them and measured to verify they are, indeed, their correct length (of 12mm or 16mm respectively) and it seems like the final count of the larger and smaller diameter heads (including bindings, second board kits, and extra bolts) is as follows:

M6x16mm:
11mm head diameter: 23 bolts
12mm head diameter: 7 bolts

M6x12mm:
11mm head diameter: 12 bolts
12mm head diameter: 8 bolts

Anyone notice this? I didn't see anything in past posts with my search. Both of my TD2 were purchased used (one from Bomber and one from private). Was there a variation based on year?

Also, I noted the bigger M8x16 bolts (to secure base plate to cant disk) have two different stampings on the head. They are split about 50/50 with the following two stampings:

FS A2-70
CS A4-70

All their size specs seem identical so are those just strength ratings?
Thanks.

[dave_f]

A2 and A4 are two different stainless alloys, to my knowledge. I believe A2 is more common, A4 is intended for more corrosive environments like marine saltwater. 70 is the tensile strength. The letters are likely the manufacturer's code. There are A1 to A5 alloys.

Incidentally, stainless bolts have a limited service life and will eventually fatigue and fail if subjected to dynamic loads. That's why you will never find stainless bolts in critical places like brake calipers, etc.

For high performance applications you could use titanium, but they also are subject to fatigue failure. Replace regularly or just do what everyone does and use good quality plated steel fasteners.

[D-Sub]

funny...just caught this the other day. smaller head diameters. made me go "hmmm" but I couldnt bring myself to post on it (believe that?)

[Chris Houghton]

Nope, we don't believe that for even a second.

[fin]

chadx,

Good observation on the M6 screw heads. Those screws are custom made for us so that we can have a 5mm hex socket on all the hardware on the TD2 screws. They are made using a cold-forming process that allows us to keep the cost down but does have some variation in the tolerance on the head diameter. We can do this as the diameter is not as critical as the socket angle itself.

Also, we done about 3 batches of these over the past years so you will also see some variations between the batches.

These differences are cosmetic and do not effect the performance or the thread engagement of the screw.

[chadx]

Thanks, Fin. In my experience, the variation hadn't seem to make a performance difference, but I'm happy to have that confirmed. Thanks. The smaller one just seemed to look a little tidier, if that makes sense.

D-Sub, Glad to hear I'm not the only one that noticed. As for the not posting, I think ralann summed it up best.:biggthump

And thanks DaveF on the your info, too.

Does anyone replace their bolts with concerns of stress/failure? I would assume our application doesn't cause the type of loads that warrant occasional replacement. I'm sure a replacement for an occasional rounded out hex head or lost bolt, but replacing for metal fatique? Anyone? Good idea or waste of money?