https://en.wikipedia.org/wiki/Countersink#Types
90deg: http://www.ebay.ca/itm/3-8-90degree-6-FLUTE-HIGH-SPEED-STEEL-CHATTERLESS-COUNTERSINK/222433723311?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649
82deg: http://www.ebay.ca/itm/IRWIN-12411-High-Speed-Steel-Countersinks-/132075555598?hash=item1ec0510b0e:g:i0wAAOSwUKxYiLzA