# Will a 1/4" rod fit a 7mm tube?



## ramaroodle (Jan 5, 2019)

I'm making a jig for use with my laser engraver.  The jig calls for a 7mm mandrel rod.  Rather than drive 25 miles to Woodcraft to spend $5 for a replacement mandrel rod I'd rather just drive 1 mile to Lowes and get a 1/4" rod.  The mandrels are .247 dia. vs .250 for a 1/4" rod.  Will that fit into a 7mm tube?  They are called "7mm mandrels" but they are called that because they fit a 7mm tube but actually measure .247".  I'm not at home so I can't check to see if a 1/4" drill bit will fit through a bushing.  Does anybody know or can check for me?  Thanks in advance.


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## dogcatcher (Jan 5, 2019)

The rods at Lowes and other stores "about" 1/4" in diameter, kind of hand grenade close, but not precision.  Will it work, no clue, can it be made to work, yes.  Chuck up a piece of the rod, and sand it down to size.  Use ATF as a wetting agent for the sandpaper, measure often, remember to keep the sandpaper moving up and down the rod to be consistent.


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## gtriever (Jan 5, 2019)

Yep, it works. I checked it with a Sierra bushing and a piece of 1/4-20 all-thread from my local True Value.


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## ramaroodle (Jan 5, 2019)

That's what I figured. Either it would fit or I can sand/grind it to fit.

Thank you both very much.


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## Sylvanite (Jan 5, 2019)

gtriever said:


> Yep, it works. I checked it with a Sierra bushing and a piece of 1/4-20 all-thread from my local True Value.


1/4-20 threaded rod is not really 1/4" in diameter.  In actuality, it is slightly less than 1/4".

A 7mm brass tube won't slip over a true 1/4" solid rod - 7mm mandrels are made from letter D  diameter rod.

That said, I have made several jigs for 7mm tubes using 1/4-20 threaded rod.

I hope that helps, 
Eric


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## ramaroodle (Jan 5, 2019)

Sylvanite said:


> gtriever said:
> 
> 
> > Yep, it works. I checked it with a Sierra bushing and a piece of 1/4-20 all-thread from my local True Value.
> ...



Yes, that absolutely helps.  Good to know. Thanks.  The devil is always in the details.  I was gonna get the threaded rod in addition to the 1/4" rod anyway so you saved me $6.


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