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Matty16 07-31-2008 09:26 PM

What size drill bit for a 5/8" Bolt?
I am building a Pergola with 5/8" Lag bolts to support the posts to the beams, and I want to make sure that the drill bit I use is not too big. What size drill bit would you use to get a 5/8" Lag Bolt through?

buletbob 07-31-2008 10:00 PM

7/16" to 1/2" for 5/8" lag screw, BOB

skymaster 07-31-2008 10:07 PM

Bob; the root diameter of any thread will be the proper size. Root diameter is the dimension of the bottom of the thread. You can Google " pilot hole for 5/8 lag bolt" and bet the exact size Here is a chart for ya.

buletbob 07-31-2008 10:23 PM

Correct skymaster Thanks for the chart. 13/32" is what they state for 5/8" lags which is 1/32" shy of 7/16" I don't think that will make that much of a difference, being that a 7/16" spade bit would be more common for a home owner or DIY'er Thanks again.

yesitsconcrete 08-01-2008 06:32 AM

you guys're makin' what little hair i have left hurt :laughing: just pick a bit that's the size of the bolt's center EXCLUDING thread height,,, threads're for pullout strength & the center's for shear,,, scheeeesch, next thing you know, i'll probably find a couple of you on the ibmwr site :whistling2:

Matty16 08-01-2008 08:05 AM

Thank you!
Thank you guys, I will use your advice. Much appreciated! I may be on here this weekend, bleeding & injured, and asking more questions as the Pergola is going up. :thumbsup:

mrbios 09-04-2008 11:15 AM


Originally Posted by yesitsconcrete (Post 144812) thing you know, i'll probably find a couple of you on the ibmwr site :whistling2:

I'm on the ibmwr site and I just had to sign up when I saw the comment. Very appropriate or should I say very fitting? I was wondering what size to drill and I knew there was a standard so I went searching in google.

My bmw is a 1992 k75s and I bought it 6 years ago. What do you ride?

yesitsconcrete 09-04-2008 12:51 PM

76 r 90/6, 82 r100rs, & fyk 85 r100rs,,, can't being myself to spend the $$$ for newer models,,, 75s is a great bike - c bars ?

apologies to the rest of the board/thread

mrbios 09-05-2008 10:36 AM

The C bars wern't big enough, I converted to the bars from RT, and I ponder going to even bigger custom bars that come back further.

I don't see many air heads in san diego, is it tought to keep them up? Are most parts available? I have done tons of work to my k75s but it runs like a top even with 62K on it.

My apologies to the rest of the board/thread as well.

maryj335 01-13-2014 09:53 PM

i have a sofa i need to drill holes in the frame to screw in legs the threaded bolt on the legs is 5/16 i also purchases tee nuts that are 5/16-18x3/8 that were recommended from leg manufacturer. i would like to know what size drill bit i need to use for this. i would appreciate any help you can give thank u mary jane

stadry 01-14-2014 09:24 AM

i'd use 1/4" :yes:

SeniorSitizen 01-14-2014 10:47 AM

If you want the two members to pull together tight you'll bore two sizes of holes concentric. The first hole ( anchor hole ) will be the root diameter of the screw through the first member and into the second member the required distance. The second boring should be the major diameter of the screw completely through the first member. This will allow the screw head and washer to pull the two members together tight. Where you'll really see the difference is with twisted warped lumber.

Sometimes good things take a little longer.

47_47 01-14-2014 12:46 PM

The hole for a 5/16" t-nut should be 3/8". The length of your t-nut is 3/8", so, I'd drill it 1/2" deep.

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