A friend of mine who specializes in musical translations looked up the word in one of her dictionaries and found "striking point". This has been confirmed by a wide range of other texts on the Web:

"When a hammer is struck repeatedly, the strings, begin to leave an impression on its face. the original face of the hammer is curved so it strikes the strings at a small specific "striking point". As the hammer becomes grooved, this point becomes wider, and the tone of the piano changes."
http://www.highpointpiano.com/pages/piano_faq.html

"Reshaping hammers by sanding is a possible, but imperfect, solution to hammer wear as it also reduces the weight of the hammers and changes the blow distance between the striking point of the hammer and the string."
http://www.mozartpiano.com/articles/care.html

"...was engineered by a scientist for proper string length, composition, and striking point of the hammer."
http://www.cantos.org/Piano/History/technical.html

This is from a custom hammer manufacturer:

String heights, (inches or millimeters) first and last, each section, height of strings from keybed (grands) at, or nearest the hammer-string contact point.

http://www.isaacpiano.com/custom.htm

This will reinforce the notion that "contact" is the word:
http://64.233.167.104/search?q=cache:vvNkUOtZDg0J:www.speech...

--------------------------------------------------
Note added at 28 mins (2008-01-17 13:58:39 GMT)
--------------------------------------------------

all 3 answers that I see so far are good