BACB28 Boeing Bushings: Specification Families Explained

Work a Boeing-program bill of materials for any length of time and you will run into part numbers that start with BAC. They look like industry standards, and they behave like industry standards at the quoting desk — but they are not. BAC callouts are Boeing company standards, and that difference changes how you source them, how you document them, and how careful you need to be with revisions. This guide focuses on the bushing families, and on BACB28 in particular — among the BAC bushing callouts we see most often in quoting activity.

What BAC Standards Are

NAS, AN, and MS standards are public, industry-level documents: any qualified manufacturer can produce to them, and the standards are maintained by industry bodies. BAC standards are different in kind. They are Boeing's internal engineering standards — the company defines the part, holds the drawing, controls its revisions, and determines which manufacturers are approved to produce it.

For a buyer, three consequences follow. First, the authoritative definition of a BACB28 bushing is a Boeing document, not something you can pull from a public standards body. Second, legitimate product comes from Boeing-qualified manufacturing sources, and the paperwork has to demonstrate that. Third, the revision in effect for your contract matters, because Boeing revises its standards and your purchase order may bind you to a specific state of the drawing. If you want the contrast with the industry-standard world, see our guide to reading NAS part numbers.

BACB28 and BACB30: The Two Families You Will Quote Most

Boeing's bushing standards cluster into families, and two of them dominate day-to-day quoting. BACB28 numbers are most often encountered on flanged press-fit bushings — the flange gives the bushing a positive seat and helps distribute bearing load at the joint face. BACB30 covers many of the sleeve and plain configurations: cylindrical press-fit bushings without a flange, used where the bore itself does all the locating.

Treat that as orientation, not gospel. These are broad families with many members, and within each one the variants differ in wall thickness, flange geometry, length range, lubrication provisions, and material system. The full callout — base number, letter codes, and dash numbers together — is the only thing that defines the part. Two callouts that share the BACB28 prefix can be entirely different bushings.

Reading the Callout: Material Letter Codes

After the family designation, BAC bushing callouts carry letter codes that select the variant — most importantly, the material. Boeing uses material letter codes such as those denoting alloy steel, CRES, or aluminum-nickel-bronze variants, and the difference of a single letter can move you between alloys with completely different strength, corrosion behavior, and galling characteristics. Dash numbers then typically size the bushing — bore, outside diameter, and length — with the exact scheme defined by the standard itself.

The procurement rule this implies: never truncate, never paraphrase. A callout copied without its letter codes is not an approximation of the part; it is a different part, or no part at all. Quote and order against the complete callout exactly as your drawing states it, and have receiving verify the markings and certificates against that same string.

Where These Bushings Fly

Bushings earn their keep at bolted and pinned joints that see rotation, oscillation, or repeated assembly — places where you want wear to happen in an inexpensive, replaceable sleeve rather than in expensive structure. On Boeing airframes, the classic homes for these families include:

• Wing structure — spar and rib attach points, where concentrated loads pass through lugs and clevis fittings.
• Flight control hinges and linkages — aileron, elevator, rudder, spoiler, and flap mechanisms that see constant small-amplitude motion.
• Landing gear joints — trunnions, drag and side brace connections, and torque links: high load, frequent inspection, periodic bushing replacement.
• Actuator attach fittings — where hydraulic actuators meet structure and every load cycle passes through a pin joint.

The same logic drives MRO demand: overhaul intervals routinely include bushing replacement, and approved repair schemes often call for a bushing to restore a worn bore rather than scrapping the parent part.

Why Traceability and Revision Control Matter More for BAC Parts

Every aerospace part deserves a clean paper trail, but company-standard parts raise the stakes:

• Boeing controls the definition. Your contract or drawing may bind a specific revision, and the documentation should demonstrate that the product conforms to the state of the standard your contract requires.
• Qualified sources only. Legitimate BAC hardware comes from manufacturers approved for the standard, and the certification chain has to show it — a generic certificate naming no manufacturer is worth very little for a BAC part.
• Premium callouts attract fraud. Boeing part numbers carry program demand, and that is exactly the profile counterfeiters target — see our article on AS6081 counterfeit controls.
• Program flow-downs. Boeing-program work pushes traceability and record-retention clauses down the supply chain, and your distributor must be able to honor them — the core of what an AS9120 certification audits.

This is the practical case for buying BAC hardware through an AS9120-certified distributor: the audited controls — source verification, lot control, splitting, certificate pass-through — are what keep a BACB28 bushing's identity intact between the qualified manufacturer and your receiving dock.

How to Source BACB28 Bushings

When you are ready to buy:

1. Start from the full callout on your drawing — every letter, every dash number — plus any revision and traceability clauses your contract imposes.
2. Search by part number. Instaparts' catalog spans more than 266,000 aerospace parts; browse the bushings category or start from our aerospace bushings overview.
3. Get a fast online quote and review lead time and minimum order quantity against your need date.
4. Check the documentation promise before you order: every Instaparts shipment includes a certificate of conformance with full traceability.