However you want to spell it, you know what I mean!  
This listing is for 3 lengths at ~200mm which is a total of ~600mm.  
Black tack is a non-setting mouldable  fixing putty for holding motors, wires, decoders, speakers, figures, loco crew (no glue marks), leds, scenery. Great for putting on the screwdriver tip to hold screws and anything else you can think of.  It has a lot firmer hold than Blu Tack. 
It can be reused, is removable and doesn't dry.  The more it is worked and kneeded in your fingers, the stickier it gets.  Whatever surface you use it on must be grease and dust free. 
There is no packaging as such, as I cut it from a roll.