What do the following words have in common?

TAN
BAND
WRING
GRAVY
REVISED

HINT:
The same two letters, in the same order, will change each word into a new one.

Answer:

Adding or inserting the letters IT will change each word into a new one:

TITAN
BANDIT
WRITING
GRAVITY
REVISITED 

Credit: NY Times Crossword
Joe DiPietro
DROP IT!