Watch out for Chinese Bolts

[Phil Waterman]

Be careful of where you purchase hardware. Check the box and check the hardware for markings. Just bought boxes of 5/16ths bolts, nuts, washers and lock washers at the local hardware store. All of them marked grade 5. I’m reassembling the Pattern 12 sheet metal and was loose fitting all of the bits. When I went back with the air-ratchet, air pressure set at about 40 PSI, started tightening bolts down and breaking them off. Now I could see breaking 5/16 and 3/8 s if I was using the impact driver turned all the way up but air-ratchets just don’t put out that much torque.

Then went back and checked some 3/8ths nuts removing them to check the treads I discovered that the bottoms of the nuts are mushroomed out. Also found that the threads on some of the bolts had been flatten going through two layers of sheet metal.

Buying the hardware there was just convenient because it was on the way back from the gym. Now I got to figure out which bolts came from where and check the markings.

Guess I’m back to buying grade 8 bolts by the pound from the local tractor dealer $4.30 a pound what ever size. I had been using grade 8s for all the chassis now I’ll use them for everything.

[Lynn Eades]

Over here in New Zealand, I have recently seen Chinese made UNF/UNC bolts with a "class" grading. For those who don't know, Imperial bolts are (tensile strength wise) catagorised by a "grade" whereas a metric bolt is catagorised under a "class" To give you some idea a "class"8.8 metric bolt is about the same tensile strength as a "grade"5 imperial bolt.
So what may have happened is that you have asked for grade 5 bolts, and the supplier has sold you class 5.5 imperial bolts which will have a tensile strength akin to margarine.
Grade 5 = class 8.8
grade 8 = class 10.6
Hope this helps.

[Phil Waterman]

Lynn - I love your strenght rateing.

So what may have happened is that you have asked for grade 5 bolts, and the supplier has sold you class 5.5 imperial bolts which will have a tensile strength akin to margarine.

That was about all these bolts were good for is bolting a sandwich together.

[rob love]

There were senate hearings in the US a number of years back, regarding bolt forgeries. The US army had problems with flywheels coming off M109s, and certain buildings had to have all the bolts replaced after forgeries were found.
Chinese steel (along with may other chinese produced products) seems very hit or miss. One only has to use some of the Princess auto wrenches or pullers to find that out.


I remember seeing UNC/UNF bolts with the metric markings when I was in Cypress 15 years ago.