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Buna-N O-Ring Kits
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allorings.com, Inc.
PO Box 64
Hampton Falls, NH 03844
Fax# 603-843-6743

Automated O-Ring Insertion Equipment

O-rings used for sealing straight thread
tube fittings on a boss.

The standard sizes for O-rings include 20 sizes used to seal straight-thread tube fittings on a boss.  A boss is cylindrical projection on a casting or forging.  The end of that projection is machined to provide a flat, smooth surface for sealing.  Straight threads used with an O-ring provide a better seal than tapered threads used alone. 

The 900 series of dash numbers identifies the 20 sizes of boss seals.  Except for size -901, the digits after the 9 identify the nominal tube size in 16ths of an inch.  The tube size is its outside diameter (OD).  For example, size -903 is intended for use with 3/16-inch tube.  The one exception, size -901, is intended for use with 3/32-inch tube.   1/16-inch tube is not common in aircraft use.