Why You Want ARP Bolts for Your Engine

arp bolts ARP is the first thing you think of when you need fasteners for your race engine. Need some head bolts? Call ARP. Need a complete fastener kit? Call ARP. Or go online to Summit or JEGS if you don't have a convenient local speed shop that's an official ARP dealer. The point is that ARP is everyone's racing fastener company. And they have been for many years.

ARPOccupying eight separate locations in and around scenic Santa Paula and Ventura, California Automotive Racing Products provides standard and custom fasteners for engine builders and motorsports customers around the world. ARP is one of the most advanced fastener technology companies on the planet. This becomes abundantly clear when you tour its 115,000 square foot facilities.

What's not directly on display is the engineering and science that go into every ARP fastener and the reason why they need so many different machines and processes to make the best racing fasteners available. The engineers spec these procedures and there are scientifically valid reasons behind each and every one of them. The technicians and employees all follow rigid procedures to make sure each fastener is the highest quality possible. It goes beyond material strength to also include straightness, heat treat and hardness, surface finish, thread type, fastener head to shank radii, lubrication, packaging and numerous other details that apply to individual fasteners to ensure they are the best possible part to accomplish a given task.

ARPEvery nut, bolt, stud and fastener is manufactured to exacting predefined standards for that particular part. It's based on the strength and clamping requirements of the fastener per application and finalized with ARP's own steep benchmark for core materials, machining, heat treat and quality control. All ARP coils and bar stock are shipped from Carpenter Technology foundry in Reading, Pennsylvania. ARP Director of Sales and Marketing Chris Raschke says they are the world's premium factory for these materials and they consistently meet ARP's exacting quality requirements.

Spotlessly clean machines
straighten, cut and cold forge
the wire into bolts and studs.

In addition to premium grade standard materials, ARP also specifies its own proprietary alloys specifically formulated to meet target strength and yield characteristics as required. For example they specify 8740 chromoly steel in the top two available grades, (SDF and CHQ) for the huge coils or wire used to make nuts and bolts and the bar stock for studs. All of this is defined by the strength of their engineering department where a staggering degree of science and expertise is brought to bear managing the fastener process from design, metallurgy and materials, testing and evaluation, installation procedures and direct customer interaction to track fastener performance at every level. The term aerospace is applied to many racing products, but ARP long ago recognized that aerospace quality is nowhere near good enough for a racing environment, thus they seek to exceed aerospace standards by a wide margin.

ARP facilities set the standard for cleanliness and organized efficiency. When you
see how its done it leaves little doubt you are witnessing some of the highest
caliber fastener technology in the world, aerospace included.

ARP is the primary fastener supplier to virtually all forms of motorsports from Formula 1, NASCAR and NHRA professional ranks right down to your local Saturday night sportsman competitors and of course every hot rod, sports car and street machine out there. Founded in the sixties by Gary Holzapfel, an aerospace fastener engineer who recognized the need for dependable high quality fasteners throughout the motorsports community. He also understood that the rigors of competition often match and exceed most aerospace requirements and he was determined to produce the finest quality fasteners possible to serve the motorsports community. ARP now occupies a leadership position across the full spectrum of motorsports and high performance street activities.

Hot and Cold Heading Processes

This process takes the massive coils of proprietary wire from the raw stock warehouse and feeds them through massive machines that straighten the coiled wire and cut it into appropriate lengths for the particular fastener being formed. Each individual slug is then cold-formed (hammered) and/or induction heated into the final shape to form the head of the bolt. As seen here the five step process delivers bolt cores ready for threading, forming the radius at the head to shank interface and final heat treating.

Giant coils of alloy specific wire are fed into machines that straighten and cut the
wire to specified lengths. Then the machines hammer the bolt head onto the
individual slugs and they are deposited into trays for transport to the threading
and heat treating facilities.

DSC_5678Larger fasteners are fashioned in a massive Toco long-stroke, single-die, cold forging machine. The Toco is reserved for larger specialty parts such as DuraMax head studs and parts up to 12 inches in length and .600-inch diameter. The inclusive hot head process straightens the wire, heats and cuts it to length and adds the installation hex all at once.

The Toco straightens the wire, cuts it and adds the installation hex to each stud.
Here you see a finished stud blank being ejected into the collection bin.

Heat Treating

After shaping the parts to the correct dimensions they are heat-treated with specific processes for each type of part. Parts are gang-loaded into an internal quench furnace (IQF) and heated to a specified temperature and length of time based on the material and the component application. The heat treating ovens are computer monitored and calibrated to ensure the exact same process for every batch. The parts are then cleaned and moved to a draw oven to adjust the Rockwell hardness to the correct spec for the type of part being treated.

ARP prides itself on the cleanliness and organization of it's facilities. And they also support other manufacturers within the industry by using their products wherever possible. The oven ignitors are equipped with high temperature MSD plug wires and boots to ensure optimum performance and reliability.

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Parts from these trays are reloaded into special bins for the ovens. Each heat
treat follows a specific recipe according to the material. The process is computer
monitored to ensure quality. Note MSD plug wire and boot on the ignitor.

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Left: Random samples are examined throughout the manufacturing process.
Right: These ladies are hand stamping the ARP logo onto rod bolts one at a time.

Polishing and Finishing

Massive vibratory tumblers use various polishing and finishing media such as walnut shells, cork, various polishing stones to deburr un-machined parts and polish specialty parts like stainless bolts and nuts. The tumblers are loaded with the appropriate media and run for a specified amount of time to provide the optimum finish specified by the engineers.

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Each tumbler is processing a different series of parts with a specific finish.
If you look closely you can see bolts tumbling within the polishing stone media.

Centerless Grinding

arp boltsThe centerless grinding process ensures perfect concentricity on all studs prior to the threading process.. Before this can take place the parts have to be thoroughly cleaned of scale and corrosion remnants left over from the previous heat treating process. This is accomplished in special shotpeening machines where scale and corrosion are removed and the parts are bombarded with .0017-inch stainless steel shot to prep them for grinding. Multiple machines like this one run full time prepping parts for the grinding department. There are many different machines in the grinding section to handle all the different types and sizes of studs.

The main floor is covered with centerless grinding machines literally grinding out thousands of components for the threading machines. The grinding wheels are constantly monitored to ensure that they are dressed correctly to grind the components to a .0001-inch tolerance. These hand -ed machines grind the pieces one at a time. From here components are cold headed, straightened, and broached. The ARP logo is stamped, followed by heat treating, shot peening, straightening check and then ground to the final diameter.

Centerless grinding is a hand-fed process that requires careful attention to detail
to ensure safety and precise components for the threading machines.


Thread-rolling is performed to MIL-S-8879A specs after the heat treat. This dramatically increases the fatigue strength by a factor up to 10 times greater than fasteners threaded prior to the proprietary heat treat operation. Rolled thread are significantly stronger that cut threads and the floor is fill with dedicated thread rolling machines for every type of fastener.


The thread rolling section covers a large area of the main shop. Each station
performs a specific threading operation and conducts regular quality checks.


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These large tanks hold the solutions
that apply the black oxide coating.

After the threads are rolled most ARP fasteners are either polished or black oxide coated for a finished appearance. Most of the fasteners operate within a non-corrosive environment so a black oxide coating is applied to provide a uniform appearance. The coatings offer no real protective qualities, but they do enhance the appearance of the parts and suggests the high degree of quality built into them.

Nut Forging

Nuts are forged from the raw wire fed into a straightening and forming machine that forms hex-shaped and 12-point nuts. The nuts are forged to a tolerance of .001-inch which far exceeds aerospace requirements. Enforcing a very close-tolerance fit between the bolt/stud and nut ensures more accurate clamping force and helps the nut resist fatigue. The forged blanks feed into CNC-threading machines to tap the threads. Raschke says the tolerances are held to five times better than aerospace standards. Chromoly nuts are then transferred to metal finishing for black-oxide coating. Stainless nuts go to the polishing stations. According to Raschke, nuts are much harder to manufacture than bolts and studs. They require exacting tolerances because they incorporate so little material.

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Massive coils of raw wire are straightened and fed into the machines that forge
the nut's shape and punch the center hole. Tolerance is held to .001". Nuts are
then heat treated, tapped and black oxided.

Quality Control

Quality control is one of the most important aspects of the manufacturing process and ARP takes it very seriously. A well equipped control lab is maintained to regularly inspect and test parts pulled from the production runs. Every hundredth part is tested against the defined standard. The machines in the lab allow destructive and non-destructive testing as well as microscopic inspection of shapes and surface qualities.

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ARP's advanced test lab regularly tests and documents the strength and quality ARP parts. Here you see a test jig pulling a stud until it fails. Results are stored and graphed on the computer screen. In the center, a comparator inspects the shape of a finished part and compares it to the standard.

arp boltsARP cuts no corners in its manufacturing procedures and the result is very high quality fasteners for every application. They make fasteners for all popular engines and other motorsports applications and the maintain an ongoing engagement with customers who require special fasteners for new engines and other applications. They will make parts for any requirements and work with customers to fill all of their fastener needs regardless of brand, type or origin. ARP wants to be your fastener company and in most cases they already are. And now that you have seen what goes into the process, you can better appreciate the quality and durability you're getting.

You're not paying extra for just nuts and bolts. You're paying a fair price for the absolute best quality parts money can buy. That applies to your engine parts, your brakes, wheel studs and the whole range of motorsports fasteners they make available to you. They also serialize fasteners for some customers like Formula 1 and IndyCar teams, connecting rod manufacturers and others who want to keep close tabs on every fastener and how it is used. And while they're at it they also make specialty fasteners for unnamed aerospace companies and military requirements. If that sounds like just what you need for your high performance engine or project click the ARP ad at the top of this story and order your free 2015 catalog. You might be surprised at what else they have available for your personal projects.

Photography by Annie Furgerson, John Baechtel and ARP

Automotive Racing Products (ARP)
1863 Eastman Avenue
Ventura, CA 93003
800) 826-3045