I purchased a D1-4 chuck without the three pins, figuring they would be
common and cheap. I found that there are no standards for the thread end and
the set I got from Ebay for around $50 with shipping did not fit. I finally
got a set that fit from Grizzly for a bit over $66 with shipping. Moral: if
you do lose them, check the threads and your wallet before purchasing.

Don Young