HL12 hiloks

HL12 are sometimes used where there is significant tension load on the fastener. Otherwise there is no benefit of the extra head weight.

HL11's are reduced shear flush heads (should never be used in composite parts)
HL10s and HL12s are protruding heads
HL523s are shear flush heads
HL13s are tension flush heads

Where I work... HL pins/collars often replace old fashioned swaged collar lockbolts... which mostly had protruding flush tension head pins. Exceptions occurred when the structure was altered/modified/repairs... THEN protruding and flush shear heads HL pins were specified.

An HL12(nom) or HL112(1OS) or HL412(2OS) can always replace HL10(nom) or HL110(1OS) or HL410(2OS)... + mating collar...

The USAF shop pretty much adopted HL11, HL12 and HL13 [+1OS, 2OS] Pins with aluminum shear or tension collars to match the head type. SO HL12/HL112/HL412 PINs [and their mating collars] were long ago deemed suitable replacements for HL10/HL110/HL410 [and their mating/shorter collars]... with just a very few exceptions**.

This simplifies the HL PN [pin and shear collar + oversizes] to fewer 'types'/NSNs'... and de-confuses the shops... since there is NOW 'just' protruding-tension head HL PINs for all protruding head installs. for every [99%] protruding head application. AND the minor weight increase is is of zero concern... since titanium is ~70% for the mass-weight of the steel pins they replace.

** exceptions ONLY where the shorter threads and collars of the HL10 installation is/are needed for threaded tail protrusion interference.


Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

@SWComposites

Can you clarify why you would not use reduced shear flush heads in composites? What would you use instead?

Re reduced shear head fasteners (HL11 head types):
- the fastener head is VERY small (reminds me of a finishing nail)
- the laminate pull thru load is low
- its relatively easy to over torque the fastener and pull the head into or thru the laminate or facesheet, resulting in delaminations and other damage.

Use a standard shear head (HL523 type) or tension head fastener (HL13 type).

Flush head height to diameter ratios (approximate):
- reduced shear head, 0.25
- shear head, 0.35
- tension head, 0.45