Screw Size Confusion

Little Dorrit

Little Dorrit

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I'm doing some work on my cabin sole. I have 12mm teak and holly boards and want to put some countersunk brass tuned pattern screw cup washers in with suitable brass screws to secure them better.

I'm getting a bit confused about what size screws to use. I was thinking of M8??

However the correct countesunk cup washers however give the following spec:

No.8 ~ to fit metric screw size 4mm ~ outer diameter 10.3mm shown here

Can anyone give me any advice on the best brass screw size and appropriate cup washers please?
 
Are you mistaking M8 and screw size 8?

Screw sizes are, I think, one of those annoying leftovers from the imperial dark ages where the number "8" refers to nothing other than it being bigger than a number 6 screw and smaller than a number 10 screw.

So for the cup washers you have linked to you would drill a 10mm (or 10.3mm) hole in your boards and use a no8 x 1/2, 3/4, or whatever size screw you need to get a good purchase on the surface below your board. The 1/2. 3/4 etc screw size refers to length of screw as a fraction of one inch.

Apols if you knew all this, bit I think thats what you are asking.
 
If the sole is solid teak and holly (like mine in the picture below) I don't think that you need cup washers. I replaced the original brass screws with countersunk Torx stainless steel screws, 4 x 35mm (IIRC). They are really not obtrusive at all.

The picture is of a top that covers a small storage place beneath the sole. You can make out a similar one under the table, just above the date. The construction is like that of the rest of the sole.

HPIM0922.jpg
 
fredrussell said:
Are you mistaking M8 and screw size 8?

Screw sizes are, I think, one of those annoying leftovers from the imperial dark ages where the number "8" refers to nothing other than it being bigger than a number 6 screw and smaller than a number 10 screw.

So for the cup washers you have linked to you would drill a 10mm (or 10.3mm) hole in your boards and use a no8 x 1/2, 3/4, or whatever size screw you need to get a good purchase on the surface below your board. The 1/2. 3/4 etc screw size refers to length of screw as a fraction of one inch.

Apols if you knew all this, bit I think thats what you are asking.
Click to expand...

No apology required you have correctly interpreted my question!!

I think a No. 8 screw would be sufficient unless anyone can suggest differently.

They will need to screw a small way into the fiberglass so 2 cm length No. 8 should be ok?
 
fredrussell said:
Are you mistaking M8 and screw size 8?

Screw sizes are, I think, one of those annoying leftovers from the imperial dark ages where the number "8" refers to nothing other than it being bigger than a number 6 screw and smaller than a number 10 screw.

So for the cup washers you have linked to you would drill a 10mm (or 10.3mm) hole in your boards and use a no8 x 1/2, 3/4, or whatever size screw you need to get a good purchase on the surface below your board. The 1/2. 3/4 etc screw size refers to length of screw as a fraction of one inch.

Apols if you knew all this, bit I think thats what you are asking.
Click to expand...

If you drill a 10mm or 10.3mm hole, as suggested, the screws will fall right through. :disgust:
Regards screw sizes, think of the number as being a fraction of an inch. Thus a No 8 is 1/8" dia, a No 6 is 1/6" dia etc.
 
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