You've raised a good point of contention, and you're right to seek clarity and documentation. Here's a breakdown of the issue, the relevant code sections, and why the inspector's claim is likely incorrect.

The Core Issue: Connecting the GEC and EGC with ONLY the Bonding Screw

Your concern centers on whether the bonding screw (the one typically used to bond the enclosure to the neutral/ground busbar) provided by the manufacturer is sufficient to serve as the sole connection point for the Grounding Electrode Conductor (GEC) to the Equipment Grounding Conductor (EGC) busbar.

Why Using Only the Bonding Screw is Likely a Violation1. 250.24(A)(4) Makes Your Point

You're absolutely right to point to 250.24(A)(4). This section explicitly states that the connection between the grounded conductor (neutral) and the equipment grounding conductors

"shall be made by the use of suitable lugs, pressure connectors, terminal bars, or other approved means." The key phrase is "suitable lugs, pressure connectors, terminal bars, or other approved means." A small bonding screw is highly unlikely to qualify as any of those, especially for the often larger sizes of GECs.2. Purpose of the Bonding Screw

The primary purpose of the bonding screw is to bond the metal enclosure to the neutral/ground bus, ensuring electrical continuity between them. It's meant to carry fault current within the enclosure to quickly trip the breaker. It's not typically designed or rated to handle the full potential fault current or the continuous current that the GEC might carry under certain ground fault conditions.3.

GEC Sizing

The GEC size is based on the size of the service entrance conductors (or equivalent for separately derived systems) as per 250.66. It's rare that a bonding screw would be sized to handle the equivalent ampacity of the GEC, which can be quite large.
4.

Mechanical Integrity and Corrosion

Relying solely on a small screw for the connection between the GEC and the EGC is also a concern for mechanical integrity and potential corrosion over time. A proper lug and bolted connection, or a terminal bar, provides a much more robust and reliable connection.

Where Did the Inspector Get This Idea?

It's possible the inspector is misinterpreting the code or applying it incorrectly. Here's why the "manufacturer sized" argument is problematic: No Universal Chart for Bonding Screws as GEC Connections

There is no standard chart in the NEC or industry-wide that sizes bonding screws specifically for GEC terminations. Manufacturers typically size bonding screws for their intended purpose – bonding the enclosure to the internal grounding/neutral system. They don't generally consider it the sole point of connection for the GEC.

Listing and Labeling

If a manufacturer intended the bonding screw to be used as the sole GEC termination point, the equipment must be listed and labeled accordingly. This listing would have to demonstrate the screw's ability to safely carry the GEC's current under fault conditions, maintain mechanical integrity, and resist corrosion. It's extremely unlikely such a listing exists for standard bonding screws.

How to Challenge the Inspector's Interpretation (Respectfully and Effectively)1. Cite Specific Code Sections

Politely but firmly point out 250.24(A)(4). Ask the inspector how the bonding screw meets the requirement of "suitable lugs, pressure connectors, terminal bars, or other approved means."2.

Ask for Documentation

Request the documentation or chart the inspector is referring to that demonstrates the bonding screw's suitability for use as the sole GEC termination point. Ask for the listing information from the manufacturer to back this claim. Ask what listing standard has been followed? (For example UL467)3.

Escalate if Necessary

If the inspector persists without providing adequate justification, politely request to speak to their supervisor for clarification. Frame it as seeking clarification on the interpretation of the code.4.

Submit a Formal Question

If you still can't get a satisfactory resolution, consider submitting a formal request for interpretation to your local AHJ (Authority Having Jurisdiction) or even to the NEC itself (through the NFPA).

The Correct Way to Connect the GEC Terminate to the EGC Busbar with a Listed Lug

The correct method is to use a listed and appropriately sized lug (based on the GEC size and the lug's listing) to terminate the GEC directly to the EGC busbar. Ensure the lug is properly torqued according to the manufacturer's instructions.

In Summary

Your understanding of the code is correct. Using only* the manufacturer's bonding screw as the sole GEC termination point is highly unlikely to meet NEC requirements. You need to terminate the GEC to the EGC busbar using a listed lug, pressure connector, or terminal bar. Back up your position with the relevant code sections, and politely challenge the inspector's interpretation by asking for documentation to support their claim. Good luck! Flag for review