I don't know about steel bolts but brass ones I have found are not generally free machining. I think the threads are rolled so a different grade is used – I think CZ121 is best for machining, the stuff used in bolts etc is more sticky.

Bolts are made to a specification, and any metal that does the job can be used to make them. The steels found in different bolts is likely to be similar, but there are no guarantees. Might machine OK or be difficult. An obvious example is 8.8 stainless steel bolts aren't made from the same alloy as ordinary 8.8 steel bolts.

Brass is different again. Main advantage is low corrosion with good heat and electrical conductivity. Brass isn't first choice for strength. There are a multitude of different brasses. Common 60:40 has a yield strength of 95MPa, compared with steels which range between 200 and 1200MPa. I'd expect a Brass bolt to be only half as strong as steel at best, and considerably weaker than a 8.8 or better bolt.

Dave

When making jigs and fixtures for RR we had to use unbrako made socket screws where required and proof was supplied. We found other makes had slightly different head sizes and somtimes the socket was a diferent size for the Allen key. We didn't have any tests for materials.

David

Hi Keith,

Ordinary 8.8 bolts are often made from (unalloyed) steel with 0.35 to 0.45% C, the 10.9 and 12.9 bolts are usually made from steels alloyed with Chromium or Chromium and Molybdenum.

Thor

Years ago I tried turning down some shanked M10 bolts from the local DIY supermarket. The material was horrible. It was not a substitute for mild steel bar (free cutting or not).

One could say "What was I to expect".

JA

Come back to me when you have a tracable source. That table is titled "stainless steel" but the content says "carbon steel". ASME SA324 does not exist. It is a supplier website of dubious veracity.

An 8.8 bolt is by definition high tensile steel. Minimum tensile strength 800 MPa. Stainless steels are lower than this, typically 500 to 700 MPa for common grades. A4 is used for some fasteners and is available in 800 MPa minimum tensile strength (A4-80). However this does not meet the 660 MPa minimum yield strength of the 8.8 specification.

Robert.

As for using bolts as stock to turn things out of, seems like they are frequently lousy material to machine. Part of the problem is the thread has been rolled on there, so it is work hardened and not easy to machine. The head has been cold formed out of the original round bar the size of the shank, so it is well work hardened too. The plain shank in between the thread and the head is sometimes OK.

I suspect the effect would be worse on brass bolts and screws.

In the 1960's the chippies who worked alongside me at a shop fitting company always kept a bar of hard soap to lubricate screws, it something I've continued doing myself, My father was taught this in the RAF as well

Hand soap is likely to cause corrosion in some combinations of wood and metal due to it not being PH7 (neutral) and including water in it. I have seen this myself so I would avoid soap and stick with wax or some other plain lubricant.

Martin C

Good stuff on leather jackets too. It certainly is greasy!