The Speedring for Rotalux Deep Octa Indirect 150 cm from Elinchrom allows positioning of an Elinchrom flash head facing inward toward the back of the modifier (indirect). The metal speedring has hinged spring-action rod sockets that allow you to initially set up the Rotalux in an untensioned state before opening it to its working size.

Even though it was not made for these two softboxes their deep design make them compatible:

Elinchrom Rotalux Deep Octabox 70cm and the Elinchrom Rotalux Deep Octabox 100cm