You can identify where a wormhole leads and what size hulls can fit through it by checking its visual appearance and/or its Show Info window.

Visual appearance ID guide.
Show Info (text-based) ID guide (click to show/hide).
Terminology note:
Right-click a wormhole and select Show Info. The top two sentences are irrelevant.

The third sentence (beginning, “This wormhole seems to lead…") narrows down the hole's destination:
The fourth sentence indicates a hole's remaining life:
The fifth indicates its remaining mass:
The last sentence indicates what size class the hole is, i.e. which types of ships will fit through.


WARNING: NOT ALL HOLES OF A PARTICULAR SIZE CLASS WILL ALLOW THE SAME NUMBER OF SHIPS THROUGH.
     That is to say: only S holes all have the same total mass limit. M, L and VL vary within their own classes.
     For example, D845s—L holes—will pass 5 million tonnes, whereas Unidentified Wormholes—also Ls—only pass 750,000 tonnes.

The jump range of wormholes is 5 km (double that of stargates/Ansiblexes).

To see how much mass a particular hole has, you must identify its type, which is the non-K162 side. Then you can Control + F on this page.
     You can also use the above link to check whether a VL is freighter-and-smaller or caps-and-smaller (but don't be dumb with either).

All frigholes are now effectively unrollable.



Unidentified or "Uni" or "Drifter" wormholes have different mechanics to normal holes and are only used for certain purposes.

A quick overview of Drifter hole mechanics.