# Proper T Nut Size?



## SamI (May 19, 2019)

Hi all,

I’m going through the tooling I got with my Bridgeport and noticed that the hold down kit is a bit on the small side. I’m going to order a new one. 

Anyway, everything I have read suggests that the T slots in a Bridgeport should be 5/8” however mine are measuring 9/16”. Ordering a suitable set shouldn’t be a problem but it does have me wondering, why are my T slots under size? Did they have different sizes throughout the years? The serial number on the head would suggest that the machine is an early 1960’s machine however I suspect that it is not the original knee installed. 

I’ve attached a picture of the table in case it’s of any use. 




Any help would be greatly appreciated.


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## Bob Korves (May 19, 2019)

Before you order any, find the dimensions, all the dimensions, of your table slots reasonably accurately, and then see if what you are considering buying might actually fit well.  For a Bridgeport it should be easy to find a set that fits nicely.  The other option is to make them yourself.  I prefer to make them from mild steel, with well rounded edges and corners, so they do not damage the t-slots, which are a part of the mill that need to stay accurate for producing accurate work.


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## SamI (May 19, 2019)

Thanks for your reply Bob. I would be tempted to make some but I also need the hold down bars and wedges etc which would be more difficult to make. 

I’ve ordered a set which should fit just fine. I’m just surprised to see that they’re not the usual 5/8” width and was wondering why. 

Thanks again!


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## projectnut (May 19, 2019)

It's hard to tell from the picture, but It looks as though the table on your mill may not be an original Bridgeport, or at least not the original to that machine.  While it has 3 T slots like he series I machines, it also has a shallow slot on the front and back similar to a Lagun or a Bridgeport series II machine.  It also appears the knee is from a different machine.  The tan color of the knee was a special order color as was the vista green.  Our high school ordered one with the tan color paint in 1965.  The standard color was battleship grey.  My 1972 machine has the standard battleship grey


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## projectnut (May 19, 2019)

I tried to edit my previous post, but exceeded the time limit.  Here's the post in its entirety.

It's hard to tell from the picture, but It looks as though the table on your mill may not be an original Bridgeport, or at least not the original to that machine.  While it has 3 T slots like the series I machines, it also has a shallow slot on the front and back similar to a Lagun or a Bridgeport series II machine.  It also appears the knee is from a different machine.  The tan color of the knee was a special order color as was the vista green.  Our high school ordered one with the tan color paint in 1965.  The standard color was battleship grey.  My 1972 machine has the standard battleship grey

Here's a link to a Lagun on eBay with a similar table:








						LAGUN FT-1 STEP PULLEY MILLING MACHINE WITH TWO VISES  | eBay
					

Find many great new & used options and get the best deals for LAGUN FT-1 STEP PULLEY MILLING MACHINE WITH TWO VISES at the best online prices at eBay! Free shipping for many products!



					www.ebay.com
				




It also appears the brake for the knee is on the front of the knee (like a Lagun) rather than the left side of the knee as on the Bridgeport series I machines


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## SamI (May 20, 2019)

Thank you for the information. I originally thought the knee was not the original but it looks as though the green has been painted over the tan. However now it looks as though the table is from a different machine. I guess I’ll never know for sure if and why it was changed.


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## NortonDommi (May 20, 2019)

Check if it is Metric, could be 14 mm which is very common.  If the table has been changed anything is possible.  As to why perhaps someone made T-nuts and didn't stake them?  That is the usual cause of breaking hunks out.


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## SamI (May 20, 2019)

It measures a perfect 9/16” so pretty confident it’s not metric. I guess it’s just the thing with older machines! Adds to the charm I suppose. Everything moves where it should and doesn’t move where it shouldn’t so aim pretty happy with the machine overall. Got a buddy to help me put the ram back on then to try and tackle the electrical issues!

It came with a VFD but it was badly wired and was also powering the X axis cross feed with no additional overload protection. What I am planning is a smaller VFD for the power feed until I change it out to a more modern version at which point the VFD will move over to my compressor!  I’ll treat this as a new install and attempt to re wire and program the VFD rather than rely on the previous owners solution. I’ve ripped out all the old wiring and switches now so that should make life a little easier!


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## NortonDommi (May 20, 2019)

SamI said:


> It measures a perfect 9/16” so pretty confident it’s not metric. I guess it’s just the thing with older machines! Adds to the charm I suppose. Everything moves where it should and doesn’t move where it shouldn’t so aim pretty happy with the machine overall. Got a buddy to help me put the ram back on then to try and tackle the electrical issues!
> 
> It came with a VFD but it was badly wired and was also powering the X axis cross feed with no additional overload protection. What I am planning is a smaller VFD for the power feed until I change it out to a more modern version at which point the VFD will move over to my compressor!  I’ll treat this as a new install and attempt to re wire and program the VFD rather than rely on the previous owners solution. I’ve ripped out all the old wiring and switches now so that should make life a little easier!


I only asked because although my country is  Metric in reality Metric and Imperial are both common so I double check everything as a SOP.
A M12 T-nut has a nominal slot dimension of 14 mm + 0.2 - 0.3 and 9/16" is 14.2875 mm.  Probably 1/2" then.  At least you can still easily buy both.


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