# United States tariff line 8540.99.40.00: Electron guns; radio frequency (RF) interaction structures for microwave tubes of subheadings 8540.71 through 8540.79, inclusive

> In the United States tariff, line 8540.99.40.00 covers parts, electron guns; radio frequency (RF) interaction structures for microwave tubes of subheadings 8540.71 through 8540.79, inclusive. Goods under this line enter free of general (MFN) duty. It falls under HS subheading 8540.99 in heading 85.40 (chapter 85).

Source: https://border.bot/countries/united-states/hs-codes/8540994000
Last updated: 9 October 2026

[Countries](https://border.bot/countries) / [United States](https://border.bot/countries/united-states) / [Chapter 85](https://border.bot/countries/united-states/hs-codes/85) / [8540.99](https://border.bot/countries/united-states/hs-codes/854099) / [8540.99.40.00](https://border.bot/countries/united-states/hs-codes/8540994000)

## Key facts

- Tariff line: 8540.99.40.00
- Covers: Parts, electron guns; radio frequency (RF) interaction structures for microwave tubes of subheadings 8540.71 through 8540.79, inclusive
- Duty (MFN): Free
- Additional duties: None recorded
- Restrictions: None recorded
- Tariff: [United States](https://border.bot/countries/united-states)
- HS subheading: [8540.99](https://border.bot/hs-codes/854099)

## What this line covers

In the United States tariff, line 8540.99.40.00 covers parts, electron guns; radio frequency (RF) interaction structures for microwave tubes of subheadings 8540.71 through 8540.79, inclusive.

Its legal text is “Electron guns; radio frequency (RF) interaction structures for microwave tubes of subheadings 8540.71 through 8540.79, inclusive”, read under “Parts” and “Other”.

## How it is structured

It falls under HS subheading 8540.99 in heading 85.40 (chapter 85). The first six digits are the Harmonized System code; the 4 digits after them are added by the United States tariff.

- Chapter 85: Electrical machinery and equipment and parts thereof; sound recorders and reproducers, television image and sound recorders and reproducers, and parts and accessories of such articles
- Heading 85.40: Thermionic, cold cathode or photocathode tubes (for example, vacuum or vapor or gas filled tubes, mercury arc rectifying tubes, cathode-ray tubes, television camera tubes); parts thereof
- Subheading 8540.99: Parts
- Within the subheading: Other
- Line 8540.99.40.00: Electron guns; radio frequency (RF) interaction structures for microwave tubes of subheadings 8540.71 through 8540.79, inclusive

## Duty

Goods under this line enter free of general (MFN) duty.

## In other countries

No other national tariff on border.bot has live lines under 8540.99 yet.

- [The Harmonized System text for 8540.99](https://border.bot/hs-codes/854099)

## Other lines under 8540.99

- [8540.99.80.00](https://border.bot/countries/united-states/hs-codes/8540998000) Other

- Previous line: [8540.91.50.00](https://border.bot/countries/united-states/hs-codes/8540915000) Other
- Next line: [8540.99.80.00](https://border.bot/countries/united-states/hs-codes/8540998000) Other

## Frequently asked questions

### What does tariff line 8540.99.40.00 cover in the United States tariff?

In the United States tariff, line 8540.99.40.00 covers parts, electron guns; radio frequency (RF) interaction structures for microwave tubes of subheadings 8540.71 through 8540.79, inclusive.

### What is the general (MFN) duty on 8540.99.40.00 in the United States?

Goods under this line enter free of general (MFN) duty.

## Sources and updates

The tariff lines for the United States come from border.bot release 1 (edition 2026HTSRev21), read from the publisher’s files, and have been live since 9 October 2026.

The duty rates for the United States come from border.bot release 1 (edition 2026HTSRev21), read from the publisher’s files, and have been live since 9 October 2026.

The trade programmes for the United States come from border.bot release 1 (edition 2026HTSRev21), read from the publisher’s files, and have been live since 9 October 2026.

This page was last updated on 9 October 2026.

Guidance from published tariff data, not a binding ruling. For a decision customs must follow, apply to the destination’s customs authority for a binding tariff ruling.

Official source files:

- https://hts.usitc.gov/reststop/exportList?from=0000000000&to=9999999999&format=CSV&styles=false

Machine-readable: https://border.bot/countries/united-states/hs-codes/8540994000.json