IIRC, its an 18mm and a 21mm but its been a while since I've done it so don't hold me to that. The smaller size is for the pins and the larger one holds the carriage on. Make sure you have some locktite for the carriage bolts. They come with locktite from the factory and I've heard a story of someone loosing a bolt because they didn't put the locktite on when they reinstalled the bolts!
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