Stroke thickness as in Illustrator

[theoutside (Kyle Houchens)]

this is now a feature in v8, you can define a line thickness and add taper or control the cap shape.

see this link

Rhino 8 Feature: Linetype Enhancements

[plan view radio 2] Linetype Enhancements Linetypes for Rhino 8 have been enhanced beyond a simple dash pattern. These enhancements include join styles, cap styles, and new width properties. Unlike traditional patterns and simple print widths, enhanced linetypes can draw stylized curves with both width and taper. Document and Object Linetypes Existing Linetypes can be customized or new linetypes copied in Options under Document Properties on the Linetypes page. Custom linetypes are referenc…