Hex Lag Screws are used to fasten wood and/or metal pieces to each other and can also be used to affix items to concrete or masonry when combined with lag expansion shields. Lag screws feature a heavy-duty construction and usually have a hex head type to facilitate installation with a simple hand wrench. Full assortments of #3661 contain eight (8) refills comprised of Hillman item numbers #3662 - #3669.