A part of their modular Astro T-2 system, the 0.3mm Alpine Astronomical Baader T-2 Aluminum Fine-Adjustment Ring is a very thin spacer ring that is used to fine-tune your rig during eyepiece projection astrophotography techniques. The ring is machined out of aluminum to be strong yet durable, and is made without threads for easy installation and removal. The ring also offers the added benefit of preventing binding between two threaded parts to make disassembly faster and easier without damaging your gear. The 0.3mm thickness equates to roughly 2/5 turn of rotation. Alpine offers three sizes of the spacer ring, and each is color coded for easy identification—this size is colored black.