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What is the pin above the gas tube hole used for? — 4 Answers

by Kane, from AL, United States Asked on January 28, 2020

Name JL Billet AR 15 Lightweight Billet Upper Receiver (4.3)
$224.95 $202.46 Save 10%
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Answered by Thisguyoverhere, member, from OR, United States, on June 16, 2020

The hole on top of the gas tube is for an anti rotation pin when using a JL Billet handguard. Pay close attention to this upper, it has flared areas behind the barrel nut threads and is not mil-spec. Only select handguards including the JL Billet rails will work without modifying the upper. I'm speaking from personal experience, I own several JL Billet lowers and uppers.

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Answered by William, member, from AZ, United States, on September 20, 2020

It's an alignment/anti-rotation pin for the handguard.

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Answered by Grendel, member, from OR, United States, on August 25, 2020

It is an alignment/anti rotation pin for no billet handgaurd.

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Answered by Tom, member, from KY, United States, on July 25, 2020

Some Handgaurds have a hole in them at the same point. It’s like an index pin. It will be straight.

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Last updated 2026-08-10 UTC.