NYLON INSERTS 101 – PART 2

by Bobby D.S. Wright of

Tramec Continental-Aero

UNDERSIZED NYLON INSERT

• Physical Appearance: nylon mushrooms or expands upward as the mating end protrudes through the nylon.

• Possibility of Root Cause: Approximately 8% of nylon issues are considered undersized nylon inner diameter, whereas the opening of the nylon insert is too small and when the mating end tries to protrude through the nylon, it mushrooms/expands to compensate the width of the mating end.

POPPING/MELTING NYLON INSERT

• Physical Appearance: the nylon insert will literally pop out of the nut and/or melting of the nylon occurs during installation.

• Possibility of Root Cause: Approximately 90% of nylon issues are considered popping out/melted due to the End User’s installation practices of installing too fast and too far down on the mating end. (See installation requirements slide).

OFF-CENTER NYLON INSERT

• Physical Appearance: the nylon insert appears to not be centered.

• Possibility of Root Cause: Another rarity as the off-center nylon insert does not affect the functionality of the part, because of its memory and resilience. Nylon serves as an excellent locking feature. The perpendicularity of the tapped hole is key to guiding the mating end through the nylon insert. The mating end threads are pushed against the nylon while being torqued and are securely locked as the nylon material tries to return to its original form.

INSTALLATION REQUIREMENTS

• Installing nylon insert locknuts should not exceed the Prevailing Torque of 1st On by the Industrial Fasteners Institute (IFI) Prevailing Torque Requirements.• For example; a 5/8-11 nylon insert locknut (full, heavy or thin

and even an all-metal (with a locking feature)) has a 420 in/lb Maximum for 1st On. Converting the in/lb to ft/lbs is: 34.99 ft/lb Maximum.

• Unfortunately, you can not convert in/lb and ft/lb into RPMS, because in/lbs and ft/lbs are measurements of torque, whereas, RPMs is a unit of force.

• Per NASM 25027, sub-clause 6.1.2 Installed – a nut is considered installed when one (1) or two (2) bolt threads, excluding the bolt end chamfer, protrude through the top of the nut.

360° OR 6 STAKED CLOSURE – WHICH IS THE BEST?

• There is no known scientific or industrial standard that suggests a 6 staked closure is better engineered than a full 360° closure and vice versa.  Both types of closure have the same FORM FIT AND FUNCTION of the purpose of securing the nylon insert into the nut.