You will find that these threads are a legacy from the accessories sold in the '70s and '80s by both Celestron and Meade. The visual backs sold with the SCTs had these 1.38" * 24TPI (35mm) and a variety of accessories use them. This is also the rear port thread on the original C90. There was an accessory sold for the C90 called the Large Accessory Ring (LAR) that permitted the use of the SCT visual back and other 2-24TPI accessories. The last LAR I saw go at auction brought over $80!!
Don't confuse the 127Mak with the 130. The 127 is an Orion Apex 127 in Celestron clothing. I assume the 90/102 (N4) and 130 were sourced by Synta from another OEM. The Apex 127 ring will fit the 127 Mak, but not the 90/102 (N4) and 130 with integral visual back flip mirror.
Meade sells a LAR (ETX - SCT Thread Adaptor #07036) for the ETX90/105/125, which has a SIMILAR rear port thread for about $20. However the ETX rear port is 34.6 mm and the #07036 is a bit tight on the 35 mm Celestron rear port. With some lapping it can be made to fit. Getting it back off is another issue.
The Baader NX4/C90 / ETX / SCT adapter, Part 2958500A is like the LAR, but it adds a 1.25" filter thread, so you can screw your filter in and use it with this adapter. It only seems to be sold with s female SCT thread to male T-thread adapter for about $40. Notice that they sell this for the ETX too. The Celestron 35mm will fit the Meade 34.6mm as the thread pitch is the same.
The ScopeStuff #ETXA - ETX Rear Cell Thread Adapter is similar to the Meade #07036, $31.
Edited by Geo., 08 October 2014 - 10:23 AM.