Looking for a tool ( oohharrr )

[Fivetide]

That YouTube vid got me thinking about some stuff, and I was wondering is there’s a tool that would cut a groove around the inside of a slice of ally tubing or U shape? I want to be able to cut two groves so I can slide a piece of thin plate along them. Very similar to the old wooden sliding top pencil case. I think they are called runner groves? The grove would only be 2 or 3 mm deep and about 3-4 mill tall. More than likey it would look simaler to a dremil saw attachment .. not sure but I dont seem to be able to get the search right for one on google.

[Web Goblin]

Tee slot cutter maybe.

Tee Slot Cutters - Arc Euro Trade (http://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Milling-Cutters/Tee-Slot-Cutters)

[Clive S]

Or perhaps a slitting saw.
Slitting Saws - Arc Euro Trade (http://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Slitting-Saws-and-Arbors/Slitting-Saws)

[Fivetide]

Great answers , neeeded to know what to look for and think I've found it 3mm T-slot (http://www.ebay.co.uk/itm/1Pc-Hss-AL-T-slot-End-Mill-Milling-cutter-Select-Size-From-16mmx3mm-to-32mmx8mm-/160879802575?pt=LH_DefaultDomain_3&var=&hash=item25752ef8cf) this should work side on to cut out the slot perfectly !