TMB 6 mm SWA 58 Degree TMB Planetary
The "TMB 6mm" primarily refers to the popular TMB Planetary II 6mm eyepiece for telescopes, known for good value, wide 58° Field of View (FOV), decent sharpness for its price, and comfortable eye relief, offering brighter, easier viewing than orthoscopics or Plössls, though genuine ones are better than many clones. It's a compact, 1.25" diameter eyepiece with fully multi-coated optics, popular for planetary and lunar viewing, delivering solid performance often compared favorably to more expensive options like Orion Expanse or Tele Vue Radians. 
Key Features & Characteristics:
Type: TMB Planetary II Series Eyepiece (Thomas M. Back design).
Focal Length: 6mm.
Barrel Size: Standard 1.25" (31.75mm).
Field of View (FOV): Around 58-62 degrees (wide-angle).
Optics: 5 elements in 3 groups, fully multi-coated (FMC green) for good contrast.
Eye Relief: Long, around 16mm, making it comfortable for glasses wearers and reducing "kidney bean effect" (blackouts).
Build: Metal frame, fold-down rubber eyecup, thread for filters. 
Performance & Reputation:
Value: Considered excellent for its budget-friendly price point (around $50-$60 USD equivalent).
Image Quality: Delivers sharp details, especially on the Moon and planets, with good light transmission and color correction, outperforming simpler designs.
Comfort: Very easy and relaxing to look through, providing a more immersive view than narrower FOV eyepieces.
Comparison: Often compared to higher-end eyepieces, holding its own despite being a budget option. 
What to look for:
Genuine vs. Clones: The original TMB eyepieces (often sold by Burgess in the US) are highly regarded; beware of inferior Chinese clones.
Versions: Later versions (like the Planetary II) addressed issues like light flaring found in very early models.