NAS6604 Close Tolerance Shear Bolt, 1/4″-28 Thread, 1/4″ Dia, Alloy Steel 160 KSI; Supersedes NAS1304 and NAS1104 (Choose Grip Length)

Looking for NAS1304 or NAS1104 bolts? You are in the right place.

NAS1304 and NAS1104 are inactive for new design. NAS6604 is the current production part number and is the direct replacement. The dash number does not change, as they have the same grip, same overall length, same 1/4″-28 thread, same alloy steel, same 160 KSI minimum tensile rating, same cadmium plating. For most use cases in motorsports, robotics, and aerospace, NAS6604 and NAS1304 can all be treated as functionally the same.
Note that NAS1104 and NAS6204 are the short-thread sibling of NAS6604, 1/32″ less thread. Unless you have major clearance constraints and need that additional 1/32″ of space via the reduced thread length, it is safer to use either an NAS6604 or NAS1304 bolt given the addition nominal thread length.

Older car build manuals, chassis parts lists, aircraft maintenance manuals and kit hardware bags very often still call out the NAS1304 or NAS1104 number because that is what was current when the document was written. Those bolts have simply been renumbered. You have not been given the wrong part — use the size chart below to find your dash number.

Bolts are sold individually.

Specifications

Size Chart — NAS6604 Grip and Length, with NAS1304 / NAS1104 Cross-Reference

The first three columns are what you are buying: the NAS6604 part number and its grip and overall length. The next two columns show the superseded numbers that same bolt replaces — if your manual or plans call out either of those, order the NAS6604 number on the same row.

How to Read the Dash Number

The dash number is the grip length in sixteenths of an inch — the length of the unthreaded shank. A NAS6604-16 has a 1.000″ grip. Overall length runs longer than the grip by the thread length. Size the bolt so the grip matches the total thickness of the parts being clamped, with the threads starting just outside the hole.

Why a close tolerance bolt?

The shank of a close tolerance bolt is ground to a tight diameter tolerance so it fills a reamed hole with a light interference or transition fit. That eliminates the slop an ordinary AN bolt leaves in the hole, so load transfers through the shank in shear rather than letting the joint work and elongate the hole. This is why suspension pickups, wing attach points, and other primary structure call for NAS6604 rather than an AN bolt. These bolts are also substantially stronger than AN hardware — 160 KSI minimum tensile versus 125 KSI for a standard AN bolt.

What does 160 KSI mean?

KSI is thousands of pounds per square inch, so 160 KSI is 160,000 psi minimum ultimate tensile strength — the stress at which the material finally fails. It is a property of the steel, not of the size, so every dash number in this series carries the same 160 KSI rating; the larger sizes simply have more cross section. Note that ultimate strength is not working load: a properly torqued bolt is already carrying significant preload, and any design should apply an appropriate safety factor.

Drilled and Corrosion Resistant Options

Every bolt on this page is the standard undrilled version — solid shank, solid dished hex head, no safety wire or cotter pin holes. This is the configuration called out by the great majority of drawings and parts lists, and it is what ships when you order a plain NAS6604-dash number.

The same bolt is manufactured in drilled and corrosion resistant configurations under modified part numbers. We do not stock these, but we can quote and order any of them — contact us with the part number:

Note the letter goes before the dash number and replaces the hyphen: a drilled shank NAS6604-16 is written NAS6604D16, not NAS6604-16D. Drilled versions carry their own NSNs and are not interchangeable with the undrilled part for certification purposes.

One Practical Check When Substituting

Grip and overall length are the same between the old and new numbers, but thread length has been observed to vary very slightly between older and current production runs. If you are replacing a bolt in an existing assembly and the nut reaches the end of the threads before you reach specified torque, add a washer to take up the difference. This is normal and is not a sign you received the wrong bolt.

Also Available

We carry the companion diameters in this same close tolerance shear bolt series:

• NAS6605 — 5/16″-24 thread, 5/16″ diameter. Supersedes NAS1305 and NAS1105.
• NAS6606 — 3/8″-24 thread, 3/8″ diameter. Supersedes NAS1306 and NAS1106.

Need a drilled shank, drilled head, corrosion resistant version, or a dash size not shown as stocked? Contact us and we will quote it.