You can achieve the desired extension length by combining multiple extenders of different lengths.The length of the extension ring is 4mm, 5mm, 6mm, 7mm, 8mm, 9mm.Outer diameter: 60mmExternal thread length: 3mm4mm-female thread length is 3mm5mm-female thread length is 4mm6mm-internal thread length is 4.5mm7mm internal thread length is 5.5mm8mm internal thread length is 6mm9mm internal thread length is 7mmfeature:1. External thread - M54*0.75. Internal thread - M54*0.75, eliminating a series of focusing problems.2. The extension tube has M54*0.75 internal thread and M54*0.75 external thread, which can elegantly solve the spacing problem in astronomical photography.3. Use this extension tube to get the correct image ratio or exact spacing required for reducers or magnetic field flatteners.4. All-metal structure and anodized aluminum process, durable.5. The desired spacing can be achieved by combining several extenders of different lengths, you can use 1, 2, 3, 4, 5 or 6 extension rings as needed.Package Contents:1x M54*0.75 extension tube kit length 4mm 5mm 6mm 7mm 8mm 9mmAbove package contents only, other products not included.Please Note: Lighting and different displays may cause the color of the item in the picture slightly different from the real item. The allowed measurement error is +/- 1-3cm.