Washers.. m8.. m10 etc

[kaseryn]

I'm looking around screwfix for washers and don't really understand the sizes..

for instance

http://www.screwfix.com/prods/17038/Bolts/Washers/Flat-Washers-BZP-M10-Pack-of-100


those are listed as form A, m10

so is that a 10mm internal diamater? If so.. how do i know the overall diameter?



others listed as eg m8x25 .. so is that 8mm internal and 25mm external?



much thanks

 

[Burnerman]

An M10 washer is one that will pass over a 10mm thread, so in effect the hole in the middle is a fraction larger.
There is a formula that governs the washer diameter compared with the hexagon nut that compresses it - I forget the exact equation but the washer is meant to be about 10% bigger than the hexagon point.
Large washers - which are meant to spread the load - are called 'penny' washers because of their oversize diameter. So, your 8 x 25 will be 25mm in diameter.
Time to polish the anorak! This is the sort of things we had to know to become a member of the 'Institute'.......!
John

 

[kaseryn]

I see thanks..

so with the m8x25.. is that for an 8mm internal thread?

 

[Burnerman]

An M8 washer will pass over a male M8 thread with minimal clearance.
John

 

[kaseryn]

Ok, got it now.. thanks

 

[Thermo]

An M10 washer is one that will pass over a 10mm thread, so in effect the hole in the middle is a fraction larger.
There is a formula that governs the washer diameter compared with the hexagon nut that compresses it - I forget the exact equation but the washer is meant to be about 10% bigger than the hexagon point.
Large washers - which are meant to spread the load - are called 'penny' washers because of their oversize diameter. So, your 8 x 25 will be 25mm in diameter.
Time to polish the anorak! This is the sort of things we had to know to become a member of the 'Institute'.......!
John

is that the institute of washers and nuts and bolts and stuff?

 

[Burnerman]

An M10 washer is one that will pass over a 10mm thread, so in effect the hole in the middle is a fraction larger.
There is a formula that governs the washer diameter compared with the hexagon nut that compresses it - I forget the exact equation but the washer is meant to be about 10% bigger than the hexagon point.
Large washers - which are meant to spread the load - are called 'penny' washers because of their oversize diameter. So, your 8 x 25 will be 25mm in diameter.
Time to polish the anorak! This is the sort of things we had to know to become a member of the 'Institute'.......!
John

is that the institute of washers and nuts and bolts and stuff?

Whey hey thats near enough.....a member of institute of mechanical engineers (mechies) is a bit closer
John