Minimum Thread Protrusion

Safe Load Program don’t have a specific standard for the correct installation of bolts and fasteners for ancillary fittings used on tanks and tankers in our industry, but simply turn to basic engineering practices for our guide.

When Installing bolts complete with nuts washers spring washers, self-locking nuts, etc, we have a basic requirement for minimum a thread protrusion to ensure that all the threads in the fastener are engaged.

• Threaded fasteners, when installed and tightened, should protrude a minimum distance of at least one thread beyond the top of the nut or plastic insert, any unthreaded chamfer or crown must not be considered in this thread count/protrusion.

Industry “Basic Principle“

• The simple rule is that two full threads should protrude above the face of the nut, this method ensures that all the threads in the nut are engaged.

There may however be situations where two full threads simply cannot be maintained due to limitations in component assembly.

• Excessive thread protrusion should be avoided.
  • Where possible, the number of threads protruding should not exceed five.
  • In no case should thread protrusion exceed ten threads.
• Self-locking nuts; where the distance from the top of the nut to the locking element (plastic insert) is equal to or greater than the bolt chamfer or crown, the bolt or stud end may end flush with the top of the nut.
• A good rule to follow is to always use the shortest standard-length fastener that gives a minimum one thread protrusion.

SLP Manager
Lee Stringer