The hi-lok fastener system, the HL18, HL19, HL20, HL21 pins and the HL70 collar.The hi-lok fasteners are the second most used fasteners in structural assembly of aircraft's after the solid rivets MS20470 and MS20426. Why? What are the characteristics that makes this fastener the second choice after the solid rivets? Hi-lok fasteners are defined by a pin and a collar. The pin is similar to a screw and the collar to a nut. The assembly of the pin, and the collar makes the hi-lock fastener system. The pin is like a screw but with additional advantages regarding a simple screw. The collar is not a simple nut, but a special nut with unique properties. What are the reasons to use this type of fasteners? The reasons are simple and can be summarize to the following properties: 1. Higher tension and shear strength, the material used and the geometry of the fastener gives him the best properties regarding strength. 2. Lightweight fasteners, the hi-lok system as the best relation between weight and strength regarding the assembly between two elements. Better that the use of screws and nuts. 3. Easy and quick assembly, with the specific tools the assembly time is must lower that the rivet or screws/nut assembly time. The assembly is very easy with no complex steps and the final assembly is always perfect with no defects. 4. Good stress concentration factor, the specific geometry of the pin element gives to the hole an increase in fatigue life, much better that if we use the screw/nut system. 5. Fastener cost, accessible and cost effective element in the installation on the aircraft. 6. Correct torque application, the collar property gives us the guaranty that the correct torque is applied to the assembly, removing the problem of vibration, strength and fatigue of the pin itself. These are the mains advantages of the hi-lok fasteners. These fasteners are property of the hi-shear corporation, the company that develops this fastener. For that reason the standard designation of these fasteners is defined by the HL letters. the -5 number defines the diameter of the fastener per multiples of 32inchs ( diameter =5/32 =0. The HL letters define that we are specifying an Hi-lok fastener. the collar as a similar P/N. Therefore HL18 is pin and HL70 is a collar. There exist NAS or specific manufacturer specification that are equivalent to the HL designation. The P/N is specified by the sequencing letters and numbers: HL18PB-5-16. . We apply the torque to a specific part of the collar. we insert the pin in the hole. If you need to specify the hi-lok system in your assembly you must request the pin and the collar P/N and not only the pin P/N. we apply the collar to the pin and apply torque with the required tool. Generally the P/N is defined by the Hi-lok manufacturer company Part number. the number 70 defines the material and geometry of the collar and the -5 defines the diameter in multiples of 32inch (diameter=5/32=0. the letter HL defines the hi-lok system. the number 18 specify the geometry and material of the fastener.156 in). The hi-lok is the same but the NAS system or the manufacturer company internal systems adopts different numbering system to identify the hi-lok part number.156 in) and the -16 defines the grip length of the fastener per multiples of 16 inchs (length = 16/16= 1 in). The quantity of fasteners is so great that we can find numbers from 1 to 1000 in the material/geometry designation. This P/N is only to the pin. The most used collar is the HL70-5. the letter PB defines the finish protection of the fastener. During the installation of this hi-lok fastener system we need access to both sides of the structure. with or without interference depending of the target of the hi-lok ( shear or tension application). geometry and material is defined by the numbers 18 and 70. that presents a small increment in diameter just used for hi-lok repairs. not requiring additional supervision to confirm the correct torque value. The HL18 is the shear protruding pin. defined by a specific number after the HL letters. That means that if you do repairs to aircraft's and you need to replace a HL18PB-6 pin because the hole as cracks or is oversize. After dividing the pins for tension and shear they can be also divided in protruding head or countersunk head pins. the HL20 is the tension protruding pin. the HL19 is the shear countersunk pin and the HL 21 is the countersunk pin. HL20 and HL21. You must select the tension pins when the main load applied is tension and shear pins when the shear is the dominant load. HL19. In shear application select the diameter of the pin according to the standard procedure: . This part of the collar that breaks permits that the correct torque be applied to the installation. There are several type of pins and several type of collars. you must select the correct one. The most used hi-loks are the HL18. depending of the application. The permanent part of the collar will continue with the pin in the assembly. They are called the 1st and 2nd oversize hi-lok pins. Each normal hi-lok fasteners system diameter as two oversize fasteners that can replace the first diameter in case of a repair or damage to the hole. We can divide the hi-loks pins for tension and shear application. You do not need to select the next hi-lok pin diameter the HL18PB-7. You must use the 1st oversize of the HL18PB-6.this part of the collar will break at the correct torque value. The tension pins have greater heads than the shear pins. pdf .gen-aircraft-hardware. That means that in your joint.the upper higher shear strength of the bearing load failure of the plate.com/images/pdf/hilok.com/fastener_hl_stds.asp?pagename=hiloks http://www. In tension application use the hi-lok with adequate tension ultimate strength for the assembly.hi-shear. The hi-lok must present a higher shear strength than the bearing of the plate used. the failure criterion used must be the plate bearing failure. For that use the closer diameter of the fastener that guaranties the failure of the assembly by bearing and not by fastener shear.htm http://www.gen-aircraft-hardware. http://www.com/template.