Holes are one of the most common features in a model and a physical part.  There are nearly endless reasons why one would want a hole and hundreds of ways of creating that hole.  

Knowing this, it is imperative that drawing calls out the exact hole the designer intends, otherwise you can get 99% accuracy with 100% failure.

• Dimension

  • <DIM>

  • Value of the number

• Diameter

  • Ø - <MOD-DIAM>

• Blind

  • ↧  - <MOD-DEPTH>

  • Drilled hole, uses drill-bit which has an angled tip 

• Countersink

  • ⌵ - <HOLE-SINK>

  • Think of how ships SINK gradually

• Counterbore

  • ⌴ - <HOLE-SPOT>

  • Think of a BOREd that has square edges.  Use these BOREds to create a staircase, or steps

• Through All

  • THRU ALL

  • Drill through everything!

  • Through All - Both -  Goes into the paper and up out of the paper

• Up To Next

  • THRU

  • Stop drilling when you break through the first wall

• Up To Vertex/Surface

• Offset From Surface

  • Same as blind, but instead of measuring from the start point, you measure from the end point

• Up To Body

  • Though all bodies until it reaches the selected body

• Mid-Plane

  • Blind into and out of the paper in equal proportions