A paper label displaying a Smith & Wesson K Frame Model 66 Strain Screw Square Butt used part, with the text 'K Frame Model 66 Strain Screw Square Butt', '357 Magnum Stainless Steel', 'Strain Screw', and 'Square Butt'. There is a small screw on display in front of the label.

Smith & Wesson K Frame Model 66 Strain Screw Square Butt Old Style .357 Magnum Used - 66172A

$6.99
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A paper label displaying a Smith & Wesson K Frame Model 66 Strain Screw Square Butt used part, with the text 'K Frame Model 66 Strain Screw Square Butt', '357 Magnum Stainless Steel', 'Strain Screw', and 'Square Butt'. There is a small screw on display in front of the label.
  • A paper label displaying a Smith & Wesson K Frame Model 66 Strain Screw Square Butt used part, with the text 'K Frame Model 66 Strain Screw Square Butt', '357 Magnum Stainless Steel', 'Strain Screw', and 'Square Butt'. There is a small screw on display in front of the label.
  • Smith & Wesson K Frame Model 66 Strain Screw Square Butt Old Style .357 Magnum Used - 66172A
  • Smith & Wesson K Frame Model 66 Strain Screw Square Butt Old Style .357 Magnum Used - 66172A
  • Smith & Wesson K Frame Model 66 Strain Screw Square Butt Old Style .357 Magnum Used - 66172A
  • Smith & Wesson K Frame Model 66 Strain Screw Square Butt Old Style .357 Magnum Used - 66172A
  • A paper label displaying a Smith & Wesson K Frame Model 66 Strain Screw Square Butt used part, with the text 'K Frame Model 66 Strain Screw Square Butt', '357 Magnum Stainless Steel', 'Strain Screw', and 'Square Butt'. There is a small screw on display in front of the label.
  • Smith & Wesson K Frame Model 66 Strain Screw Square Butt Old Style .357 Magnum Used - 66172A
  • Smith & Wesson K Frame Model 66 Strain Screw Square Butt Old Style .357 Magnum Used - 66172A
  • Smith & Wesson K Frame Model 66 Strain Screw Square Butt Old Style .357 Magnum Used - 66172A
  • Smith & Wesson K Frame Model 66 Strain Screw Square Butt Old Style .357 Magnum Used - 66172A
Smith & Wesson K Frame Model 66 Strain Screw Square Butt Old Style .357 Magnum Used - 66172A

Smith & Wesson K Frame Model 66 Strain Screw Square Butt Old Style .357 Magnum Used - 66172A

$6.99

Smith & Wesson K Frame Model 66 Strain Screw — Used OEM Part

Genuine Smith & Wesson factory strain screw for the K Frame Model 66 revolver, chambered in .357 Magnum. Square butt configuration, old style. Stainless steel. Removed from a used firearm and in good working condition. A direct OEM replacement for a worn, damaged, or missing strain screw.

The strain screw secures the mainspring (hammer spring) to the grip frame and directly influences trigger pull weight. Tightening increases spring tension for more reliable ignition; backing it out slightly can reduce trigger pull for target or competition use.

Part Details

  • Part Number: 66172A
  • Condition: Used OEM
  • Frame: K Frame
  • Compatible Model: Model 66 (.357 Magnum)
  • Grip Frame: Square Butt
  • Style: Old Style
  • Material: Stainless Steel

Compatibility Note

This is the old style strain screw for square butt K Frame Model 66 revolvers. Verify your grip frame configuration before ordering — round butt and square butt strain screws differ, and old and new style are not interchangeable. To find your model number, swing out the cylinder and check the frame behind the yoke.

Installation

Strain screw replacement requires removal of the grip. Installation by a qualified gunsmith is recommended.

Questions? Call or email us — we carry new, used, and new old stock S&W parts for the full K Frame lineup.

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