Originally Posted by
lysander
I love it when marketing types try to make their ads sound "technical" . . .
"Mil Spec Extractor
4140 Steel per ASTM A108, cold drawn and stress relieved BHN 187-229
Mil Spec Gas Key
4130 Profile Extruded Steel
Grade 8 Hardware"
I hope their extractor is not Brinell 187-229. That is soft, annealed soft, about a 9 on the Rockwell C scale.
After heat treatment the extractor should be Rockwell C42 to C44
And the infamous, and misunderstood "Grade 8" bolt . . .
First, the only fastener specification that has Grade 8 in it is SAE J429 which deals with hex head bolts and studs, and the "Grade 8" bolts and stud start at 1/4 nominal thread diameter. I am pretty sure you don't have a 1/4 bolt holding your gas key on.
Second, if we just take the material strength requirements for "Grade 8" bolts, that means they are made from a steel with a minimum tensile strength of 150,000 psi. The actual screw per the Army's drawings is a item peculiar screw made from a nonstandard (screw) steel and with a nonstandard head, but we'll skip that fact for the moment and look at the standard "mil-spec" screws that are the closest the the 8448508 (19200) drawing. These screws would be the Aerospace Industries Association National Aerospace Standard NAS1351 - Screw, Cap, Socket Head, Undrilled and Drilled . . . yada, yada".
NAS1351 screws are required to be made from steel with a minimum yield strength of 180,000 psi.
In fact, all of your MS and MIL-S socket head cap screws are required to be made from steels with a minimum yield strength of 170,000 to 180,000 psi, 10% to 20% stronger than your "Grade 8".
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