The short answer is that there is no functional difference between them. Gas springs, gas struts, and gas props are simply different names for the exact same mechanical device. It can be frustrating when you are shopping for parts or trying to fix something, but manufacturers and mechanics use these terms interchangeably.

The name people use usually just depends on the industry they work in or the specific way the device is being used. Here is a breakdown of how the terminology is typically applied.

1. Gas Spring (The Technical Term)

This is the most accurate, general, and universally accepted engineering term for the device. It emphasizes the function of the part: it acts as a spring, but instead of using coiled metal to store energy, it uses compressed gas.

• How it works: A piston rod moves inside a sealed cylinder filled with pressurized nitrogen gas and a small amount of oil. When you push the rod in, the gas compresses, storing energy. When you let go, the gas expands, pushing the rod back out. The oil lubricates the seals and provides a smooth, damped motion at the end of the stroke.
  

2. Gas Strut (The Automotive & Structural Term)

The word 'strut' implies a structural component designed to resist compression along its length. You will almost always hear this term used in the automotive and heavy machinery industries.

• Common Uses: Holding up the heavy metal tailgate (hatchback) of a car, keeping a car hood open, or supporting the doors on a tractor cab.
  
• The Vibe: When people say 'gas strut,' they are usually referring to a heavy-duty gas spring that is doing the hard work of lifting and supporting a heavy load.
  

3. Gas Prop (The Cabinetry & Marine Term)

The word 'prop' implies something used to hold an object up or keep it open. This term is most common in cabinetry, marine applications (boats), and lighter-duty DIY projects.

• Common Uses: Holding open a heavy wooden toy box lid, keeping an overhead kitchen cabinet open, or propping up a storage hatch on a boat.
  
• The Vibe: When people say 'gas prop,' they are usually thinking of a lighter-duty gas spring used specifically to keep a lid or door from slamming on someone's fingers.
  

Summary

If you are trying to replace a worn-out part, do not worry about whether the box says 'spring,' 'strut,' or 'prop.' Instead, you need to focus on matching these three specifications:

1. Extended Length: The total length from mounting point to mounting point when fully open.
   
2. Compressed Length: The length when fully closed.
   
3. Force/Pressure Rating: Usually measured in Newtons (N) or pounds (lbs). This tells you how much weight the device can lift or hold open. (e.g., a 100N gas spring provides about 22 lbs of force).