After three suits have been bid, a Snapdragon Double shows 5 cards in the fourth suit plus tolerance for overcaller's suit, and 6+ HCPs.
Tolerance usually means either 3 low cards or 2 to a high honor, such as Kx. Some people play it to mean only 3 low, not honor-x.
Double shows 5 Hearts and either 3 low or honor-x Diamonds.
such as K73 KT832 862 95.