The Quadra Stepper is an extension adapter that allows a BlueSCSI DB25 to be connected to the rear DB25 SCSI port of Macintosh IIcx, IIci, Quadra Series(Q700, Q650), IIvx, IIvi, and Power Macintosh 7x00 series computers.
 
Please download the instruction manual here here

This Does Not Compute introduced the Quadra Stepper in his YouTube video, this video clearly explains how to assemble and use the product. 
He even designed the perfect shell case. Thank you, Colin!
 
Kit Version / $8 USD
Includes:
1 PCB
2 DB25 connectors (1 male, 1 female)
⚠️Important Note: "Male" and "Female" markings are silkscreened on the back of the PCB. Please be very careful, as it will not function if installed in reverse.
 
The LED and resistor are optional and not included.
If you wish to install an LED, use a 1206-size resistor in the 330 Ω to 1 kΩ range. The appropriate resistance value depends on the LED's current requirements.
Important:The SJ1 solder jumper should normally be bridged. This supplies +5 V TERMPWR to the SCSI bus. *Many modern SCSI devices draw their power from the TERMPWR.
 
Fully Assembled Version / $12 USD
Fully assembled
Tested on actual hardware
Includes a blue power LED