11 2 X shows spades
1 2 2 X shows diamonds
1 2 2 X shows hearts

1 1 1 X shows clubs

There are, of course, the many other combinations.

Some suggest the double shows at least 'tolerance' for partner's suit (2 cards in the suit).

The point requirement depends on the vulnerability and suit length..

Why not just bid the suit?
Bidding that fourth suit for some is forcing and shows a better hand.
Bidding that fourth suit shows at least 5 cards in the suit.

Discuss with partner the minimum suit length and point count requirements for the double.