Bulkhead Sizes

[nicky1200]

So i have a 6ft tank which has a built in overflow in the center of the tank and has 2 drilled holes in the bottom of the overflow which i have messered has 55mm each. The holes was drilled by the makers of the tank.So i went out and bought a 50mm bulkhead and was told i need a 65mm hole in my tank even tho the thread on the bulkhead is 50mm they told me i need a 65mm hole.
 
So now the bottom of my tank has cracked and im ordering a new pane of glass and i need to know the size of the holes i need so they can drill them.So my pipe work is 50mm pvc pipe.
 
If i get a 50mm bulkhead what size hole do i need ?Because the nut on the bulkhead is 65mm so if i had a 65mm hole then the bulkhead would just drop though. so i don't understand what they mean by 50mm bulkhead = 65mm hole when the nut on the bulkhead is 65mm....

 

[Man of fish]

Why not just drill it 50 mm and try and fit it? You can always go bigger, but you can never go smaller. Without glueing on more glass.

 

[nicky1200]

Why not just drill it 50 mm and try and fit it? You can always go bigger, but you can never go smaller. Without glueing on more glass.

Because if i get it drilled 50mm then they would deliver the glass ( 6ft ) and then if it was two small i would need to send it back off to get drilled again.
I have been told by the shop who  im buying the glass off that they can drill any hole up to 50mm for free so the shop im buying the glass off are drilling the holes for me ( save me cracking the tank ) So i need a size of the hole to tell them.

 

[DrRob]

Tank connectors are confusing beasties.
 
Most of them fit two different sizes of pipe on each side, generally solvent weld sizes. If you've got 50mm pipework then you'll have the pipe thickness and thread before you hit the flange diameter (and the nut). Different brands tend to have variations here, so it does depend slightly on where your pipework came from. Essentially you have the answer by measuring your pipework, you need a hole big enough to fit the thread through, without being bigger than the flange and washers. After a quick google most of the products out there seem to recommend between 65 and 70mm hole for a 50mm tank connector, but it sounds like yours is slightly smaller, more like the size of 40mm pipework, for which they tend to suggest a 57mm hole, which may be the hole you've got, it's close enough on the measurements.
 
Overall, if your connector fits neatly onto a 55mm hole, then get them to drill a 55mm hole. The two things these need to do is fit through the hole and have plenty of edge to seal against, so the ideal hole is a tight, but not too tight, fit.

 

[Man of fish]

Why not just drill it 50 mm and try and fit it? You can always go bigger, but you can never go smaller. Without glueing on more glass.

Because if i get it drilled 50mm then they would deliver the glass ( 6ft ) and then if it was two small i would need to send it back off to get drilled again.
I have been told by the shop who  im buying the glass off that they can drill any hole up to 50mm for free so the shop im buying the glass off are drilling the holes for me ( save me cracking the tank ) So i need a size of the hole to tell them.

Oh sorry I thought it said you were drilling it yourself.