This is a rounded exterior blend between surfaces:

When a curved surface intersects a plane surface, an edge is formed.

This is a conical-shaped recess around a hole, often used to receive a tapered screw head:

A fillet is a rounded exterior blend between surfaces.

If a plane intersects a contoured surface, no line is drawn to represent the edge.

It is not always possible to show all of the drawing views in alignment on a sheet.

This is an angled surface used on cylinders to make them easier to handle:

Knurl is a pattern form on a surface to provide for better gripping or more surface area for attachment.

Right-hand and left-hand parts are mirror images and are made to be interchangeable.

A boss is a short raised protrusion above the surface of a part.

These are used to attach parts to a cylinder so they won't turn on it:

A counterbore is a cylindrical recess around a hole, usually to receive a bolt head or nut.

A keyway is a small groove cut around the diameter of a cylinder, often where it changes diameter.

This is a flat or rounded tab protruding from a surface, usually to provide a method for attachment:

Simplified conventional representations that deviate from true orthographic projection may be used to enhance economy and clarity in a drawing.

A plane surface cannot intersect or be tangent to a contoured surface.

This is a hollow cylinder that is often used as a protective sleeve or guide or as a bearing:

A lug is a flattened collar or rim around a cylindrical part to allow for attachment.

Small curves called runouts are used to represent fillets that connect with plane surfaces tangent to cylinders.