Stamped bolt 'sizes'

[pcatterall]

perhaps some of us would benefit from a little education.
Just ordered some SS hex bolts. I ordered M16 70mm expecting bolts of 16mm diam and 70mm long but the items delivered were 170mm long x13mm.
The bolts are stamped A2-70 ( for my camper not boat) The 16mm bolts that I am replacing are stamped TY 8.8. Not sure if this is just a mistake from the supplier but would appreciate a bit of help in understanding what we should see stamped on the head of bolts.

 

[Norman_E]

I don't know why you received the wrong bolts but if you asked for M16 x 70mm hex head bolts, that is what you should have received, the only other specification is material, and for stainless steel the choices are A4, which is marine grade or A2 which is not, generally either 316 or 304 stainless steel. The 8.8 on your old bolts refers to tensile strength, and is a medium grade carbon steel bolt. See here http://www.westfieldfasteners.co.uk/Ref_Strength_Spec.html I don't know if A2 stainless bolts are actually as strong as that.

EDIT: They have given you A2 class 70 bolts rather than A2 70mm. Apart from getting the correct size, if the tensile strength is critical you would need A2 class 80 bolts to exceed the strength of 8.8 grade carbon steel. The wrong size you received could be something as simple as the result of the wrong bolts being in the suppliers parts bin, or a wrongly labelled bin.

 

[superheat6k]

perhaps some of us would benefit from a little education.
Just ordered some SS hex bolts. I ordered M16 70mm expecting bolts of 16mm diam and 70mm long but the items delivered were 170mm long x13mm.
The bolts are stamped A2-70 ( for my camper not boat) The 16mm bolts that I am replacing are stamped TY 8.8. Not sure if this is just a mistake from the supplier but would appreciate a bit of help in understanding what we should see stamped on the head of bolts.

Looks like they got your order wrong - SS M16x70 is perfectly adequate as the main description, although they could deliver any available grade of stainless. 8.8 refers to the tensile strength (high). I think A2 refers to the grade of stainless of your original bolts.

 

[vyv_cox]

Most of your answer is in Norman E's link. Your 8.8 bolts are a fairly standard heat treated carbon steel widely used in automotive applications. The first figure 8 is the tensile strength in Mpa/100 (800) and the second is the proportion of YS to UTS (80%).

The stainless steel ones are A2, AISI 304 that have been cold worked to increase strength. Their UTS is 70 x 10 = 700 Mpa

I cannot explain why the dimensions should be different, sounds like a cockup.

 

[gordmac]

If the ones you are replacing are marked 8.8 I don't think they will be stainless.