This is a genuine Teledyne Firth Sterling SI MDUNL 204F round shank indexable boring bar. Teledyne Firth Sterling was a well-known American manufacturer of industrial cutting tools (later acquired/merged).

Key Specifications:

• Model: SI MDUNL 204F
• Tool Type: Round shank indexable boring bar for turning and internal/external applications
• Shank: 1.25" diameter round shank
• Holding method: Lever/pin clamp with hex socket screw (common on older industrial holders)
• Insert Compatibility: Negative rake 55° diamond inserts (DNMG 432 and equivalent negative rake diamond inserts)
• Configuration: Right Hand

This style of holder was commonly used for general turning, boring, and facing operations where negative rake geometry provides good strength and heat resistance. The lever clamp system offers reliable insert retention.

What’s included: The complete toolholder with the installed negative rake triangular insert. No original packaging.