You know, you think I would know since I own a pair of Cor 15's. Great pump by the way. I started with one for a return on my 210 gallon then after watching some BRS videos one of them suggested using the same pump, if possible, for a skimmer and use has a backup. Made sense to me so I recently brought another Cor 15 online just for that. Glad I did. Anyway, doubt I can answer your question but here is some text from one of the pages I read if it helps any.
Included fittings
Both the COR-20 and COR-15 come with all the fittings necessary for most aquarium configurations (0.75″ output, 1″ input). A 1.25” union for the output also is included, allowing you to connect the pump in a way to produce as little head loss as possible.
What’s required
Plumbing fittings, hose, pipe, etc., and some basic knowledge of plumbing. For the COR-15, you’ll need any Apex System with an available 1LINK port.
What you get with the COR-20
COR pump, COR-20 pump driver, 100W 24VDC power supply, power cord, 1.25-inch PVC union (Slip->BSPP), 1-inch slip fitting, 0.75-inch slip fitting, and a 3-foot AquaBus cable.
What you get with the COR-15
COR pump, COR-15 pump driver, 1.25-inch PVC union (Slip->BSPP), 1-inch slip fitting, 0.75-inch slip fitting, and a 6-foot 1LINK cable.
Physical dimensions (COR-20 and COR-15)
Pump: 3.875 inches wide | 4.875 inches high | 6.250 inches deep
Driver: 3 inches wide | 4 inches high | 1 inch deep