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#### Emil VolK

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General basis question. I am attaching 2 pieces of plywood (one piece on top of the other). The bottom piece is 5/8" and the top piece is 1/2". I have Deckmate screws 1 1/8" so would these be OK? In general what is the "rule of thumb " when joining woods. Should the screw go right through both pieces of wood or half way through?

you will gather I am beginner wood worker hence the basic question.

Thanks;

EMIL

#### jschaben

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##### John
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General basis question. I am attaching 2 pieces of plywood (one piece on top of the other). The bottom piece is 5/8" and the top piece is 1/2". I have Deckmate screws 1 1/8" so would these be OK? In general what is the "rule of thumb " when joining woods. Should the screw go right through both pieces of wood or half way through?

you will gather I am beginner wood worker hence the basic question.

Thanks;

EMIL
Hi Emil - Just do the math. 5/8 + 4/8 = 9/8 = 1-1/8. If you countersink the head any at all you will have the points exposed. I usually try to size screws so they penetrate 1/3 to 1/2 way into the recieving board. In this case the top piece is 1/2 (8/16) and the recieveing piece is 5/8. divide 5/8 by 2 = 5/16. 8/16 + 5/16 = 13/16. Closest screw size would be 3/4 (12/16). Hope this helps:smile:

#### cabinetman

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##### Old School
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I would figure a bit differently. I like to get as much thread in the second piece. So, I would use 7/8" screws. Most screw lengths are from the top of the head to the point.

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#### firemedic

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##### In History is the Future
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cabinetman said:
I would figure a bit differently. I like to get as much thread in the second piece. So, I would use 7/8" screws. Most screw lengths are from the top of the head to the point.

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+1... that how I look at it too... But all bs aside, it depends on the situation. Sometimes it's just what I have on hand.

~tom ...it's better to remain silent and be thought a fool than to open one's mouth and remove all doubt...

#### del schisler

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General basis question. I am attaching 2 pieces of plywood (one piece on top of the other). The bottom piece is 5/8" and the top piece is 1/2". I have Deckmate screws 1 1/8" so would these be OK? In general what is the "rule of thumb " when joining woods. Should the screw go right through both pieces of wood or half way through?

you will gather I am beginner wood worker hence the basic question.

Thanks;

EMIL
Any glue involved?? if some glue and the 7/8" screw. That will not come aprart .

#### Brian_Hinther

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Here's a blurb from McFeeley's:

There is no hard and fast rule concerning screw length requirements
. Sometimes you don’t have much choice as to length because of the construction details. In general though, the screw should always go through the thinner piece, and thread into the thicker piece. In choosing length, try to have about 2/3 of the screw threaded into the “secondary” piece, as shown. As the thickness of the lumber increases though, this ratio can be reduced so that only 1/2 of the shank is threaded into the secondary piece.

#### H. A. S.

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##### OLD DUDE AT WORK
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General basis question. I am attaching 2 pieces of plywood (one piece on top of the other). The bottom piece is 5/8" and the top piece is 1/2". I have Deckmate screws 1 1/8" so would these be OK? In general what is the "rule of thumb " when joining woods. Should the screw go right through both pieces of wood or half way through?

you will gather I am beginner wood worker hence the basic question.

Thanks;

EMIL

I would use 1" long screws.

If the heads are going to be flush, 7/8 or 1" would work. it all depends on how the screw and head are designed.

Screw measurement:

http://www.sizes.com/tools/wood_screws.htm

#### angusmdmclean

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thanks to all for the excellent replies; I should have added the screws will be in a moist environment to then I would look for screws resistant to corrosion.

#### Chaincarver Steve

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##### I wood if I could.
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I think the screw should always go through the thinner piece,too.
The screw does go "through" the thinner, or outside, piece. But you don't really want the screw threaded into the outer piece because then it makes it hard to pull the two pieces of wood tightly together. You want the screw to be able to slip in and out of the drilled hole in the outer piece and thread (screw) into the piece it's being attached to (usually into a small pilot hole).

#### Brian Hinther

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Here's an easy solution to getting the right length screws without having to drill pilot holes, etc. (again from McFeely's):

Deck screws are a good example of Optimized Thread Length. The screws normally used to install 2 x 4’s or 2 x 6’s for decking are 3 inches long and have 1 inch of unthreaded shank. Since 2 x 4 and 2 x 6 deck material is 1-1/2 inches thick, the threads bridge the joint, as shown, resulting in an uneven and unsightly surface, or screws that are over-driven trying to “pull the board down.”
ProMax® screws are different: Thread length is optimized to eliminate crossthreading, and the 1/8” length system allows use of the longest possible screw. In most cases, the smooth shank and self-drilling point allow installation without predrilling! Just select a screw that provides an unthreaded shank length equal to or slightly greater than the material thickness being fastened.