Standard DTI FAQs
You're not sure what feeler gage inspection criteria you should use
Check installation on this website.
REMEMBER - A feeler gage entry is all the way into the bolt shank. PARTIAL ENTRY OF A FEELER GAGE IS NOT AN ENTRY AT ALL.| Application | DTI & Bolt Condition | DTI Position* Turned End | DTI Position* Unturned End | Feeler Gauge to Use | |
|---|---|---|---|---|---|
| 1 | Buildings | Plain | x | .005" | |
| 2 | Buildings | Plain | x | .015" | |
| 3 | Buildings | Coated | x | x | .005" |
| 5 | Bridges | All | x | x | .005" |
*Either on the "turned" end (that is, when the DTI is located on the nut end when the nut is turned or on the head end when the head is turned) or on the "unturned" end. Note: ALWAYS separate the "turned" element, either, the head of the bolt or the nut, from the DTI using a hardened flat washer for best results.
DTI's should be compressed at least as much the following:
For uncoated bolts and DTI's where the DTI is installed under the bolt head (no flat washer), and the nut is turned to tighten, make sure a .015" feeler gage will not enter into the DTI gaps ALL THE WAY INTO THE BOLT SHANK at least half way around the DTI circumference. Half way around a (say) five bump DTI is two or three places, for instance. This means that the residual DTI gap is less than the thickness of a .015" feeler gage.
For uncoated bolts and DTI's where the DTI is installed under the bolt head with a flat washer between the bolt head and DTI*, and the nut is turned to tighten, make sure a .005" feeler gage will not enter into the DTI gaps ALL THE WAY INTO THE BOLT SHANK at least half way around the DTI circumference. Half way around a (say) five bump DTI is two or three places, for instance. This means that the residual DTI gap is less than the thickness of a .005" feeler gage.
For uncoated DTI's and bolts where the DTI is installed on the nut (turning) end, and for coated bolts and DTI's where the DTI is installed under the head and the nut is turned to tighten, make sure a .005" feeler gage will not enter ALL THE WAY INTO THE BOLT SHANK at least half way around the DTI circumference after tightening. This means that the residual DTI gap is less than the thickness of a .005" feeler gage.
For coated bolts and DTI's where the DTI is installed on the nut (turning) end, compress the DTI to the point where where the .005" feeler gage will not enter ALL THE WAY INTO THE BOLT SHANK any place around its circumference. In some rare situations even this will not ensure at least the minimum bolt preload has been achieved, so some rotation of the nut past the point where the DTI was "dead flat" will be required. The best thing to do is to check how much rotation past "dead flat" of the DTI is required, if any, at the minimum required bolt preload in a bolt tension calibrator. For a table of minimum bolt tensions see bolt tension
