<ul> <li>Front thread - M42x1 female thread</li> <li>Rear thread - M58x1 male thread</li> <li>Thickness - 5mm</li> </ul> <p>Made of high quality aluminium alloy.</p> <p>This adapter allows using M42 lenses on M58 helicoids.</p> <p>Shoulderless design means absence of extra light path that may be necessary to keep ability of infinity focus for some lenses.</p>