Cannondale Headshok 1.56" ( 1 9/16" or 39.68mm), 12cm stem, +- 5-degree rise, with a 25.4mm bar clamp threadless stem. New, $45.00/each

• 1.56" is the Cannondale proprietary diameter. Until about 2014, almost any Cannondale mountain bike with a Cannondale Headshok or Lefty fork used a Headshok 1.56" size stem.
• Depending on which way the stem is mounted on the steering tube, the stem will have either a 5-degree rise or 5-degree drop.
• Stamped on the stem near the steering tube binder bolt are these numbers: R04 10065. They can be seen in the first picture.

Side view

Here's the same stem flipped over.

Looking down at the stem from above.

The underside of the stem.