Most of the EMS parts are designed to match the universal measures such as 2-inch(50.8mm).
And the housing can be connected to other parts both by male or female fittings.
Innovation of Astronomical Telescope
正立ミラーシステム(EMS)を開発した松本龍郎のサイト。 たった2回の反射で天体望遠鏡の像を正立像にします。
Tatsuro Matsumoto; Inventor of the EMS, Erecting Mirror System. EMS offers non reversed upright image with no additional undesirable abberations.
Most of the EMS parts are designed to match the universal measures such as 2-inch(50.8mm).
And the housing can be connected to other parts both by male or female fittings.