Standard DTI FAQs
You have Twist-Off or TC bolts on a job, and yet the engineer has specified that DTI's must be used. Can both TC bolts and DTI's be used together?
Yes. On smaller diameter TC bolts, up to 7/8" diameter, with small button heads or with hex heads, the DTI's will work correctly in any orientation on the bolt assembly just like with hex bolts. For larger diameter TC bolts, especially the 1" A490 and 1 1/8" A490, the DTI must be installed on the nut end under the flat hard washer for the compression of the DTI bumps to be available to a feeler gage for inspection. If the DTI is installed under the large button heads of these TC bolts, the size of the button head impedes access to the DTI gap. Remember, a field test to see if a "usable gap" is a good idea. If there are any problems in judging the DTI bump compression because of the shape of the TC bolt head, simply put the DTI on the nut end under the hard flat washer, and tighten in this manner. An extensive ASCE treatise on TC bolts by Kulak is available on this website as a download.