Aerospace Bar and Rod: Specs, Finish, Tolerances and Inspection

Updated October 13, 2026

Bar shapes, how they are made and where they go

Bar is the stock most turned and milled aerospace parts start from. The shape and the way it was made decide how much material you machine away, how straight and round it arrives and which specification it is bought to.

The Aluminum Association's terms guide gives the North American size breaks that distributors and mills use: rod is round and bar is square, rectangular, hexagonal or octagonal, and both start at 0.375 inch. Below that the same product is called wire. The guide also separates bar by process: rolled bar is finished by hot rolling, extruded bar by extruding, and cold-finished bar by cold work, usually drawing, to get a better surface and tighter dimensions.

Two practical points. A part cut from flat bar has its grain running along the bar, so check grain direction on the drawing before substituting bar for plate. And very large rounds of titanium, nickel and steel are often forged bar or billet, which brings in forging practice and ultrasonic requirements; our forging reference covers when a forged blank is the better buy.

The specifications that govern aerospace bar

Order bar to the specification on the drawing, by alloy, condition and product form. The same alloy is often covered by different AMS documents for rolled bar, extruded bar and forgings, so a 6061 bar callout is not the same thing as a 6061 extrusion callout. The table shows status and revision as listed on SAE's site when we checked.

The difference between AMS 5662 and 5663 decides whether the shop ages 718 after machining, and our certified material guide explains it, so it is not repeated here. The point for bar buyers is simpler: the spec number names the condition you receive, so read it before you plan heat treatment or quote machining time.

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Cold finish versus hot finish, and the tolerance documents

Cold-finished bar arrives closer to size, rounder and with a cleaner surface; hot-finished bar is cheaper per pound but needs more machining stock to clean up scale, out of round and size variation. Which one you need depends on how much you plan to remove, not on the part's final tolerance.

Size limits usually live in a separate tolerance document that the material spec references, not in the material spec itself:

What this means on a buy:

• Say the finish. Hot rolled, cold drawn, turned, or centerless ground are different products with different tolerance tables. A request for "1.000 inch 17-4 bar" can be filled by any of them.
• Size the stock for the finish. Leave enough on diameter for the shop to clean up the worst case of the tolerance table, plus decarburization or surface defects on hot-finished steel.
• Hex is measured across flats. Order hex by the across flats dimension and check the corner condition, since sharp versus rounded corners changes what the wrench feature looks like after a light skim.
• Straightness matters on long parts. Bar loaders and long shafts need straight stock. If straightness is critical, state it, because a straightened bar may carry residual stress that moves after machining.

Ultrasonic inspection class callouts

Ultrasonic inspection finds internal defects in bar that no surface check will see, and the drawing or PO should name both the procedure document and the acceptance class. A class with no document, or a document with no class, cannot be inspected to.

The documents you will see on bar:

• AMS-STD-2154, the process for ultrasonic inspection of wrought metals, revision C. NASA's JSC process specification PRC-6504 records that MIL-STD-2154 was canceled on November 15, 2004, which is why older drawings that cite it now point to the AMS version.
• ASTM E2375, the practice for ultrasonic testing of wrought products, which ASTM states was adopted to replace MIL-STD-2154. It hands wrought aluminum to ASTM B594.
• AMS 2631, ultrasonic inspection of titanium alloys, revision G, June 2022, covering titanium products 0.5 inch and over in cross section.

The acceptance classes run from AAA, the most stringent, to C. NASA JSC PRC-6504 Rev. G, which invokes ASTM E2375, publishes its single discontinuity alarm levels as reference flat bottom hole diameters:

PRC-6504 states that flight hardware must be at least Class A and that drawings with different classes in different areas must be zoned. Other primes and programs set their own classes, so treat the table as one published example and use the class on your drawing.

For bar, ultrasonic inspection is normally done on the full length at the mill or by a test house before cutting. A cut piece carries that result only if the heat and piece traceability prove which bar it came from. If your class is tighter than what the stock was inspected to, plan a separate inspection, and see our nondestructive testing reference for how methods compare.

Cut sizes, heat lots and remnants

Most aerospace bar reaches a machine shop as saw-cut blanks from a distributor, and the cut is where traceability and cost are won or lost. Order the diameter and length the part needs plus a sensible machining allowance, and say whether one heat is required.

• Length and end condition. State the cut length tolerance and whether ends must be square. Saw-cut ends are not finished faces.
• One heat or several. A long run of blanks may be cut from more than one bar and more than one heat. If your first article, lot acceptance or serialization assumes a single heat, write that on the PO.
• Heat treat lot. For bar delivered heat treated, such as 718 to AMS 5663 or 17-4 in an aged condition, test results apply to a heat treatment lot. The Aluminum Association guide defines that lot as product of the same alloy, form and size processed the same way in one furnace load, so the cert should name the lot as well as the heat.
• Marking every piece. Heat or lot transfer to each blank before it leaves the saw is covered in detail on our certified material page; require it, and require the cut source to add its own C of C.
• Remnants and surplus. A remnant bar with intact marking and a matching cert can be the fastest way to a small quantity in a hard-to-find size. Without both, it is not usable for deliverable hardware.

Materials, conditions and the trade-offs

Choose bar by the alloy and the condition you want to machine in, then by what the part sees in service. The common families and what to watch for in bar form:

Alloy behavior is covered in depth in our library pages for aluminum, titanium, nickel alloys and stainless and specialty steels. Machining considerations for turned parts are on the turning and Swiss reference.

Ordering checklist for bar and rod

• Alloy, condition and material specification with revision, for example AMS 4928 for annealed Ti-6Al-4V bar
• Shape and size: diameter, across flats or width and thickness, with the finish (hot rolled, cold drawn, turned, ground)
• Tolerance document if it is not the one the material spec references, such as AMS 2241 or ANSI H35.2
• Cut length, length tolerance, quantity, and whether a single heat is required
• Ultrasonic procedure and class, for example AMS-STD-2154 Class A, and whether existing mill inspection is acceptable
• Mill test report for the delivered heat and heat treatment lot, plus the cutter's C of C; see our C of C guide
• Heat or lot number marked on every piece
• Country of melt and the DFARS clause for titanium, nickel alloys and most steels on defense work; see DFARS specialty metals
• Packaging that protects ground or precision finishes and keeps marking legible

Counterfeit and quality risks, and how to receive bar

The risks with bar are wrong alloy or condition behind a real-looking cert, paperwork that belongs to a different heat, and remnants with no history. A visual check cannot tell 17-4 in Condition A from an aged condition, or 7075-T6 from T73.

• Match the heat number on every piece to the cert before stock goes to the shelf.
• Check the cert names the same specification, condition and product form as the PO; a forging cert does not cover bar.
• Use alloy verification on unfamiliar sources and hardness or conductivity to confirm condition.
• Measure diameter and across flats against the tolerance table, and look for seams, laps and scale on hot-finished stock.
• Quarantine unmarked cut pieces; they cannot be traced.

Our receiving inspection guide covers the dock checks, and the counterfeit avoidance process covers sources outside the mill channel.

How we source bar and rod

We do not stock bar, run a saw or publish prices. We source bar for your order from mills, service centers and distributors that can show traceability to the heat, or from certified surplus when the paperwork fully supports it, flow down your spec, tolerance, ultrasonic and DFARS requirements, and check the certs against the material before shipment.

Bar usually feeds a machined part, so we can put the material and the machining on one purchase order with one point of contact, and send blanks straight to the shop. See our CNC machining service for that route and the raw material category for plate and sheet, extrusions and tubing. Shops with certified excess bar can list surplus material with us.

Request bar and rod

Send the alloy, specification, shape, size, finish, cut length, quantity and any ultrasonic class through the certified material request form. Naming the specification revision and whether one heat is required up front is what lets us tell you quickly whether a given piece of stock is usable. A person replies within one business day, and rush requests are prioritized. Use our confidentiality process if the drawing travels with the request.

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Part, quantity and date are enough to start. Drawings and the mutual NDA follow by reply, and controlled programs never send technical data through this site.

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Related

• Aerospace Plate and Sheet: Thresholds, Tempers, Tolerances and Blanks
• Aerospace Tubing: Seamless and Welded Tube by Specification
• Buying Certified Aerospace Material and Surplus Drops
• What DFARS Specialty Metals Compliance Means for a Parts Buyer

Sources

• SAE AMS 4928: Titanium Alloy Bars, Forgings and Rings, 6Al-4V, Annealed
• SAE AMS 4117: Aluminum Alloy Bars, Rolled, 6061-T6
• SAE AMS 4123: Aluminum Alloy Bars, Rolled, 7075-T6510
• SAE AMS 5643: Steel Bars and Forgings, 17Cr-4.5Ni-4Cu
• SAE AMS 2241: Tolerances, Corrosion and Heat Resistant Steel, Iron Alloy, Titanium and Titanium Alloy Bars and Wire
• SAE AMS 2251: Tolerances, Alloy Steel Bars
• SAE AMS 2631: Ultrasonic Inspection of Titanium Alloys
• SAE AMS-STD-2154C: Inspection, Ultrasonic, Wrought Metals, Process for
• ASTM E2375: Standard Practice for Ultrasonic Testing of Wrought Products
• NASA JSC PRC-6504: Process Specification for Ultrasonic Inspection of Wrought Metals
• Aluminum Association GAG Guidance Document 001: Terms and Definitions
• ANSI H35.2 overview (aluminum mill product tolerances)