ARP Bolts

ARP Bolts Fasteners and Head Stud Kits at Diesel Power Products

When your diesel build demands absolute reliability, ARP (Automotive Racing Products) delivers. Known worldwide for their premium fasteners, head studs, and engine hardware, ARP sets the industry standard for strength, precision, and performance. Trusted by professional race teams and diesel performance shops alike, ARP hardware is the foundation of high-horsepower durability.

At Diesel Power Products, we stock a full lineup of ARP products specifically engineered for Cummins, Duramax, and Powerstroke platforms. From head stud kits and main studs to rod bolts, rocker arm studs, and accessory fasteners, every ARP component is crafted from proprietary alloys and precision-machined for maximum clamping force and consistency.

Upgrading to ARP hardware ensures that your diesel engine can handle increased cylinder pressures, boost levels, and power output — without compromise. Whether you’re building a competition truck, towing rig, or high-mileage workhorse, ARP delivers peace of mind and performance that lasts.

What really is the difference between a head stud and a head bolt you may be wondering. From the factory, all engines have head bolts. As nearly anyone has seen, a “bolt” is a threaded shaft with a hexagonal head attached. These bolts thread into the respective hole and the bolt head is then torqued down on the head(s) with a great deal of the force being applied to the thread themselves. In contrast, a “stud” is only the threaded shaft that is first installed into the block. Once the stud is installed onto the block, then the head gasket and head are placed. Finally, the head stud washer and nut are placed and torqued. Due to the change in orientation of where the force is applied, a head stud will not stretch as a head bolt will commonly do, as well as the superior metals used to make ARP head studs compared to stock head bolts.

While most diesel performance enthusiast know ARP for their heads studs, they actually have a wide range of fasteners available that are far superior to their stock counterparts. From harmonic damper hardware to rod bolts, flexplate bolts, and so much more. With ARP, you can rest assured that you’re installing the best hardware on the planet.

We get a lot of calls and e-mails each day with various product, vehicle, and installation questions. Some are completely off the wall and can even catch us off guard at times, but many others are fairly routine, so we thought we'd post some of the most popular questions regarding ARP bolts and studs that can hopefully be a good resource for you.

Q: Can you install head studs without removing the head(s)?
A: That depends. If your stock head gasket is still intact, then you definitely can. This process would involve removing one bolt at a time and installing one head stud at a time. Now, it is possible that you could damage the existing head gasket during this process so we'd always heed caution when going this route, but its been accomplished successfully enough times that we can say yes, it will work.

Q: Where is ARP located?
A: ARP is located in Ventura, California where all product is manufactured (not imported).

Q: What does ARP stand for?
A: ARP stands for American Racing Products.

Q: What is the difference between ARP's 425 and 625 series head studs?
A: The short answer is that the 625's are the superior product, but both are far superior to a stock head bolt. The 425 series, which is the most common, is built from grade 8740 alloy and heat-treated to 200,000 psi. In contrast, the 625 series is manufactured from proprietary Custom Age 625+ material that has a minimum rating of 260,000 psi tensile strength.

Q: Do I need to re-torque my head studs?
A: If you follow the ARP installation instructions, there should be no need to do a re-torque. However, it may be necessary under certain circumstances if the gasket manufacturer’s instructions require it, particularly if a fire ring has been installed. ARP recommends not doing a re-torque on a hot engine.

Q: Do I need lube on my bolts or studs?
A: ARP recommends using ARP Ultra-Torque lube to ensure an even, accurate clamp load and to prevent thread galling. This is particularly important for stainless steel fasteners. The lube should be used under the head of the bolt or the bearing surface of the nut and on the threads, unless a thread sealer is used.

Q: Can I use Loctite or any thread locker instead of ARP Ultra-Torque assembly lube?
A: Yes, you can. Some engine builders use blue Loctite on the stud end that goes into the block. Do NOT use Loctite on the nuts for the head studs or main studs. Always ensure that the threads are clean prior to applying any lube. When using Loctite, make sure you assemble the parts before the Loctite cures. You can use Loctite instead of ARP Ultra-Torque, but do not use them together.

Q: Does the chamfer on the inside diameter of the washer go up or down?
A: The chamfered side of the washer goes up, towards the head of the bolt. The chamfer is there to create clearance for the radius between the bolt shank and the bolt head.

Q: Do the head studs only go in hand, or finger tight?
A: Yes, cylinder head studs are installed only hand tight. Other than the use of an allen wrench on the hex broached into the end of the stud (to ease installation, not to apply torque), use no tools to seat them in the block. However, it is extremely important to ensure that the studs are fully bottomed out in the hole in the block and not hung up on damaged or corroded threads in the block preventing the stud from being fully seated. This is often indicated when the stud threads extend past the deck surface.