Depends on the track head and the size and shape of the bulb. Some look like balls, others look like big Tylenol capsules, others look like Type-A incandesents on steroids.
I saw some at Home Depot that could fit in candelabra sockets for a chandelier or a wall sconce -- they looked like ribbed translucent vi....never you mind...you get the idea. :P
I think these bulbs look doofy - period.
And the light some of them put out is ghastly - unlike fluorecent tubes which seem to put out a more even light.
But I guess it would do for a broom closet or a basement or some other out-of-the-way place.