Milnor's notation for tangent bundle

In Milnor's "Characteristics classes" there are two notation for the tangent bundle of a smooth manifold $$M$$. i.e. $$\tau_M$$ and $$DM$$. and $$DM_x$$ for tangent space. Why he uses of two different notation for one notion? I think both of them are $$TM$$ is new books notation.

Characteristics classes, page 14, Example 2. The tangent bundle $$\tau_M$$ of a smooth manifold $$M$$. The total space of $$\tau_M$$ is the manifold $$DM$$ consisting of all pairs $$(x,v)$$ with $$x\in M$$ and $$v$$ tangent to $$M$$ at $$x$$.

To specify a bundle $$\tau_M$$, you would have to specify two topological spaces $$E$$ and $$B$$, and a projection map $$\pi$$ between them, verifying some conditions along the way.
So Milnor does exactly this, he specifies $$DM$$ as the total space, he specifies $$M$$ as the base space, then $$\pi$$, and finally goes on to show that the conditions on $$\pi$$ hold.
$$DM$$ is the total space of the bundle $$\tau_M$$. They are not the same thing.