Skin > Add Influence > 
- Geometry
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Turn Use Geometry on if you want the influence object’s shape as well as its transform attributes (translation, rotation, and scale) to influence the skin’s shape. Turn Use Geometry off if you only want the influence object’s transform attributes (translate, rotate, and scale) to influence the skin’s shape. Default is Use Geometry on.
- Dropoff
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Specifies the rate at which the influence of the influence object’s position drops as the distance from the influence object increases. Specify values between 0.1 and 100. Default is 4.0.
- Polygon Smoothness
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Specifies how accurately the smooth skin points follow a given polygonal influence object. The higher the value, the more rounded the deformation effect. Set values between 0.0 and 50.0. Default is 0.0.
- NURBS Samples
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Specifies the number of samples used to evaluate the influence of a NURBS influence object’s shape. The greater the number of samples, the more closely the smooth skin follows the influence object’s shape. Set values between 1 and 100. Default is 10.
- Weight Locking
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Specifies that you want to prevent the influence object’s weights from being changed indirectly, typically because of weight normalization during weight painting and editing (see Lock smooth skin weights). Instead, Maya holds the weights to the Default Weight. Default is off.
- Default Weight
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Specifies the default holding weight if Weight Holding is on. Default is 0.000.