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Choose your ride: RedLine or BlackLine. The RedLine (BKFLEX-4001) has a clear lens with red tread bendable TPR temples. BlackLine (BKFLEX-4001S) is a smoke lens in a black glossy frame. Both deliver on the Brass Knuckle Flex promise: a face-hugging fit — one you won’t remember to take off at the end of the day. Powerful styling powers up the one-piece, lightweight, rimless design. This fully dielectric (metal-free) eye protection features naturally curved, flexible temples devoid of metal hinges and screws — excellent for linemen or others exposed to live electric current. RedLine and BlackLine feature our standard anti-fog protection.


Certifications and characteristics

Standard anti-fog protection plus abrasion, chemical, and UV resistance. Meets demanding industry test requirements (ANSI Z87.1+, EN166UV). 

Clear lens allows maximum light transmission without changing or distorting vision or colors (91% of light passes through). 

Smoke lens provides allover tint for normal outdoor conditions (18% of light passes through). 

About RedLine and BlackLine

The bendable, flexible TPR temples provide a secure fit without creating uncomfortable pressure points, and they’re vented to improve airflow and comfort. The one-piece molded frame and nosepiece are 100% polycarbonate for strength without weight. A 9 base curve lens provides clear, crisp, and distortion-free vision and blocks 99.9% of the sun’s ultraviolet rays. 


  • High-gloss polycarbonate frame and nose pad 
  • Naturally curved, flexible temples for fit and comfort 
  • Bendable TPR temples in red or black 
  • ANSI-rated hardcoated polycarbonate lens 
  • Standard anti-fog protection 

Part Number Anti-Fog Lens Color Frame Color Accent Color
Standard Clear Clear



Standard Smoke Black Black

Roll Up Your Sleeves and Tear In

REDLINE BKFLEX-4001 Brochure (pdf)

Brass Knuckle Eye Protection Catalog (pdf)