The main distinction between square tang and rounded (round) tang rear sight assemblies—most commonly referenced with Smith & Wesson revolvers—comes down to the shape of the front extension of the sight leaf (the tang) and the corresponding frame cutout (mortise).
Key Differences
Detailed Breakdown
1. Square Tang ("Old Style")
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Design: The front portion of the sight leaf (the tang that sits flat against the top of the revolver frame) ends in a sharp, 90-degree square edge.
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Compatibility: Used on older S&W revolvers manufactured before S&W changed their frame machining processes in the early-to-mid 1990s.
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Frame Recess: These fit into a top strap mortise that is specifically milled with square corners at the front.
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Fitment Note: A square tang sight will not fit into a rounded frame recess without permanent gunsmithing modification to either the sight leaf or the frame.
2. Rounded Tang ("New Style")
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Design: The front tip of the sight tang is rounded off into a smooth curve.
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Compatibility: Introduced around 1992–1993 when S&W standardized factory drilling and tapping under the top strap for scope mounts across K, L, N, and X-frame revolvers.
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Frame Recess: Designed to fit the rounded recess milled by automated CNC machinery on modern frames.
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Fitment Note: A rounded tang sight can sometimes sit inside an old square-cornered recess, but it leaves open gaps at the corners and may not line up properly with the original screw holes.
How to Check Which One You Need
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Inspect the Frame Mortise: Remove or look closely at the front of your revolver's rear sight base:
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If the recessed slot cut into the top strap ends in sharp, square corners, you need a Square Tang.
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If the recessed slot ends in a smooth curve, you need a Rounded Tang.
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Check for Factory Drill/Tap Holes:
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Lift the rear sight leaf. If you see factory-threaded screw holes under the top strap designed for optics mounting, your frame is almost certainly the rounded tang style.
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