The threaded inserts that are embeded into the G10 in which the Scotties are screwed into are called a Keysert made by Fairchild Fasteners and distributed by Maryland Metrics phone 800-638-1830. The part number for the new installation Keysert is 73056 with a 5/16-18 internal thread and a 7/16-14 external thread. If you strip one out and want to replace with an oversized Keysert the part number is 73057 which has the 5/16-18 internal thread and a 1/2-13 external thread. Both Keyserts require a special tool for installation.
If you're installing additional inserts, you must install G10 below the keelbox flange for the inserts to screw into.
Richard Hunt has some good pics on the class site under 'tips and twists' on how to strengthen the keelbox/deck area.