Using Nut End Installation with 1 1/4" diameter or Larger DTIs
Nut end installation of DTI's, either standard or SQUIRTER® DTIs, is often preferred by erectors, since it puts the DTI on the wrench end, and it is unnecessary to hold the bolt roll see to One side, One man Installation. The DTI must be located under a hard flat ASTM F436 washer in this case, so the turning force applied to the nut does not abrade the DTI bumps rather than just compressing them. F436 washers vary in dimensions and hardness, and are not always suitable for this application.
The ASTM F436 flat hardened washers used under the nut in this situation must cover the DTI bumps even when eccentrically located to the extreme. The F436 flat washers sometimes have such a large ID that, when eccentric, they do not quite completely cover all the DTI bumps. Applied Bolting manufactures DTI's to survive even when they are used in this "unequally compressed" condition. However, the apparent DTI compression, as measured by a feeler gage, or as judged by the "Squirt event", should be checked in a Skidmore before the connections are completed see FAQ 22 . Stated succinctly, the RCSC test is .... "If there is a measurable DTI gap at 5% over minimum tension (even one entry of a feeler gage), the assembly (including the DTI) is working correctly .........."
SOLUTIONS TO THIS PROBLEM IF RELIABLE DTI BUMP COMPRESSION CANNOT BE ASSURED
- For all bolts up to and including 1 1/8" diameter, the matching ASTM F436-04 flat washer should work properly. NOTE: Old stock flat washers made to the F436-03 and earlier specs may not have the correct ID. Current F 436 flat washer production will be fine, but checking doesn't hurt. For 1 1/4" diameter and larger, consult the table here for flat washers to use for best fit on top of DTI bumps.
- Purchase special ID flat washers which are made just for this purpose. Their availability is limited, so plan ahead. Applied Bolting can assist in determining whether they will be necessary, and can find a suitable source for them. Some sizes are now stocked by Applied Bolting and can be purchased separately or as "sets" coupled with the DTI. Click here for more information
- As a workaround procedure until correct flat washers are obtained, place the DTI under the bolt head, and (unfortunately) hold the bolt head from rotating when turning the nut.
