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Bolt grades #5110558 05/20/19 08:05 PM
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Dave Sherman Offline OP
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Not too familiar with bolt grades, but I have a need to replace the blade bolt on my John Deere riding mower. Apparently the tall grass was a little too tall for it, but instead of just stalling the engine the blade bolt sheared. First the gods smiled as I managed to find the washer and blade retainer in the grass, then the gods of broken bolts were favorable as I managed to extract the rest of it from the boss with a bolt-out (first time ever!). I am just in need of a replacement metric bolt, but wondered if I should look for a specific grade.


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Re: Bolt grades [Re: Dave Sherman] #5110565 05/20/19 08:13 PM
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clinebarger Online Content
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Generally.....The bolts only job is to hold the blade to spindle.

Knowing John Deere riders.....It was probably loose from the factory LOL

Was there a grade stamped on the head of the bolt? 8.8, 10.9 etc.

Last edited by clinebarger; 05/20/19 08:15 PM.

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Re: Bolt grades [Re: Dave Sherman] #5110567 05/20/19 08:15 PM
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Dave9 Online Content
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You didn't mention the specific mower but on this page they have bolts that are grade 10.9:

https://www.greenpartstore.com/John-Deere-Blade-Bolt--19M7788_p_19287.html

If you can figure out the JD part # you can probably get the genuine bolt for $4 delivered on Amazon or eBay, if not $1-$2 at a local dealer?

Last edited by Dave9; 05/20/19 08:15 PM.
Re: Bolt grades [Re: Dave Sherman] #5110577 05/20/19 08:23 PM
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JayhawkRoy Offline
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I have found it easiest to go to the John Deere dealer with the deck model number and get replacements. Cost is minimal. I have had to replace them due to rust and rounding off and keep three extras on hand for my mower decks.

Re: Bolt grades [Re: Dave Sherman] #5110594 05/20/19 08:41 PM
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Dave Sherman Offline OP
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Can’t tell what grade it was, it just has “JD” and 3 lines stamped on the head. Yes, I could order the genuine bolt from JD online, or the local dealer might even have it in stock, but it also looks like something I could find at Lowe’s or HD. Mower is an RX75. Strangely, JD’s online parts show it as a 7/16” by 1 3/4”, but everything on the mower is metric and it has a 15mm head.

Edit: I see the dealer has it in stock for $1.98. Might as well get the real deal.

Last edited by Dave Sherman; 05/20/19 08:47 PM.

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Re: Bolt grades [Re: Dave Sherman] #5110598 05/20/19 08:45 PM
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Rand Offline
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Originally Posted by Dave Sherman
Can’t tell what grade it was, it just has “JD” and 3 lines stamped on the head. Yes, I could order the genuine bolt from JD online, or the local dealer might even have it in stock, but it also looks like something I could find at Lowe’s or HD. Mower is an RX75. Strangely, JD’s online parts show it as a 7/16” by 1 3/4”, but everything on the mower is metric and it has a 15mm head.


usually 3 lines means grade 5


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Re: Bolt grades [Re: Dave Sherman] #5110612 05/20/19 08:58 PM
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P10crew Online Content
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That is a place where when a single bolt breaks it can mame or kill. I think I would go to your John Deere dealer. Or find one that is for sure US made.

Re: Bolt grades [Re: Dave Sherman] #5110636 05/20/19 09:22 PM
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hallstevenson Online Content
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Originally Posted by Dave Sherman
I am just in need of a replacement metric bolt, but wondered if I should look for a specific grade.

Originally Posted by Dave Sherman
Can’t tell what grade it was, it just has “JD” and 3 lines stamped on the head.

Are the (3) lines in a shape kinda like this ?

..|
/ .\

If so, that's an SAE (inch) bolt, Grade 5. Honestly, you can buy these at any hardware store. If the JD dealer is convenient, $2 isn't terrible.

Also, you measured 15mm (around 0.59") across the bolt head. A 7/16-14 bolt has a 9/16" (0.56") head.

Re: Bolt grades [Re: Dave Sherman] #5110652 05/20/19 09:33 PM
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CT8 Offline
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Is the bolt grade specific to be a shear bolt?

Re: Bolt grades [Re: CT8] #5110686 05/20/19 10:08 PM
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maxdustington Offline
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Originally Posted by CT8
Is the bolt grade specific to be a shear bolt?
That would be my concern. Slap a grade 8 on there and blow the entire thing to smithereens.


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Re: Bolt grades [Re: Dave Sherman] #5110724 05/20/19 10:44 PM
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tom slick Offline
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I don’t think JD would use a shear bolt to hold on a blade spinning at 2500 rpm. From what I’ve seen blades are held on with a grade 8 or 10.9 which are similar strength.


You get what you pay for...
So keep in mind how much you paid for this advice.
Re: Bolt grades [Re: Dave Sherman] #5110757 05/20/19 11:26 PM
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Re: Bolt grades [Re: Dave Sherman] #5110944 05/21/19 07:28 AM
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tc1446 Offline
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Originally Posted by Dave Sherman
Not too familiar with bolt grades, but I have a need to replace the blade bolt on my John Deere riding mower. Apparently the tall grass was a little too tall for it, but instead of just stalling the engine the blade bolt sheared. First the gods smiled as I managed to find the washer and blade retainer in the grass, then the gods of broken bolts were favorable as I managed to extract the rest of it from the boss with a bolt-out (first time ever!). I am just in need of a replacement metric bolt, but wondered if I should look for a specific grade.


Take the threaded portion to Lowes where they have a sizer on the wall near the bolts.


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Re: Bolt grades [Re: rubberchicken] #5112386 05/22/19 01:06 PM
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Dave Sherman Offline OP
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Thanks for the info. The new bolt and the old have lines more like \ | / along 3 adjacent edges, don't know if that means the same as the 3 arranged radially. Even the parts guy at the dealer was surprised it sheared. i was afraid maybe I had over-tightened it at some point, since I switch between the mulching blade and the high lift blade in spring and fall. This time I used the torque wrench on it, and there is no way I reached the 90 foot pound spec with the wrench I was using; it would have taken considerably more effort. Anyway, it's got a shiny new OEM bolt, there was no damage when the blade let go, and I was able to coax the broken half out of the spindle.


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Re: Bolt grades [Re: Dave Sherman] #5112920 05/22/19 10:08 PM
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tom slick Offline
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3 lines on one half as you describe is SAE grade 5.2 or ASTM A325 and is a special material and heat treatment.


You get what you pay for...
So keep in mind how much you paid for this advice.
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