metric shear bolt

[john [mo]]

anybody got a source for a 4.8 grade m12x1.75 hex bolt. the metric bolts i have found are 8.8 grade. i sheared the pto bolt on my rotary cutter and i want to replace it with a soft enough bolt to protect the equipment.

 

[Anonymous-0]

My favorite source, McMaster-Carr doesn't show them in my vintage catalog. You could try their latest catalog on line www.mcmaster.com

The 12mm bolt is 0.472" diameter. A grade 2 7/16" bolt will be about 0.437" diameter. A hot dipped galvanized 7/16 might be a little fatter. A 7/16" will be a tiny bit loose, but should function as that shear bolt.

Gerald J.

 

[john [mo]]

first place i looked was mcmaster-carr. guess i will have to figure out something on my own. thats what i get for buying a imported chinese rotary cutter.

 

[Anonymous-0]

I think the 7/16" grade 2 will work just fine. It will have a tiny bit smaller cross section and grade 2 is about as soft as you can make steel. There would be just room for a sleeve made of an aluminum soda can in the hole with the 7/16" bolt.

I'm sure someone with a metal lathe could cut down a half inch grade 2 bolt to 12mm diameter and still have enough threads for a nut to hold it in.

MF balers used to use a metric bolt with a fractional thread for their shear bolt. Nope too small.

Gerald J.

 

[john [mo]]

i was thinking the same thing. a 7/16 bolt with brass shim stock sleeve. i also talked about making my own like you said out of round stock or a bigger bolt.

 

[Anonymous-0]

I'd rather use a bolt than rod stock. If the bolt maker is reputable, the bolt should be more consistent. A google search turned up this:
" The strength factor of a fastener (i.e., nuts and bolts). In US fasteners, grade 2 has a tensile strength of 60,000 psi; grade 5 = 120,000 psi; grade 7 = 133,000 psi; grade 8 = 150,000 psi; grade ASTM A574 = 170,000 psi. In metric fasteners, grade 4.8 = 60,900 psi;"

So a grade 2 SAE and a grade 4.8 metric are practically identical.

Though a 7/16" isn't all that far from 12 mm. I probably have a better supply of 1/2" so would probably go to my metal lathe about 6' from this computer.

Wouldn't the place that sold the implement keep spares for it? Or is that asking too much?

Gerald J.

 

[Anonymous-0]

You could GO to CHINA and you could stay over there your problem solved ??? this is what the people of are USA is letting come in most of the import things are junk.

 

[john [mo]]

i bought it from rural king. the store is 30 miles one way from me. no bolts listed on their webpage. no shear bolt listed in the owners manual.i saw that the metric 4.8 was a little higher than grade 2 when searching for the bolt.

 

[Anonymous-0]

60,900 vs 60,000 is not beyond the normal variations in either. These strengths aren't reproduced to three significant digits, probably only 1.5 so I read these as being essentially the same steels and heat treatment.

The slightly smaller size of the 7/16" and slightly weaker (if any) alloy will give better protection to the mower, though the shear bolt life may be a bit shorter.

The 7/16" will rattle in the hole, but after shearing a few bolts the 12mm will rattle in the hole too.

Better to avoid hitting whatever it was that sheared the bolt.

Gerald J.