This is a Wide (48mm) Low Profile T-Ring. It offers a wider light path to reduce vignetting and a shorter light path for more back-focus. A standard T-Ring for Micro 4/3 is ~37mm Deep. This Low Profile Ring is only ~10mm deep.. giving you an extra inch of Back-Fous.
(Fits Panasonic Lumix G1/G2/GH1, Olympus PEN, etc)
Our custom made "T-Minus" rings get their name from the fact that they are shorter than the "T2" standard. This is also a Wide Ring with 48mm (.75 pitch) threads. Normal T-Rings for MIL type cameras are typically 30-38mm deep. Our "T-Minus" rings are only 10mm deep. This is very useful for reflector owners who often don't have quite enough focus range to reach focus with a camera. They are also useful anytime you can use some extra focus room, such as for using a flip mirror or other accessory on a refractor. This T-Minus ring couples your camera body to a Wide (48mm) T-Adapter or other camera mount. Each camera manufacturer has a different bayonet mount, which requires a specific T-Minus Ring. These quality rings are CNC machined of aluminum with a durable black anodized finish.