We like many buy many items from Amazon, especially now since we are full-timers, where the Prime free 2-day shipping comes in handy. When I bought my Progressive EMS, which I bought through Progressive, because I recall they warned that units bought through Amazon and s few other vendors would not be warranted. But my recent experience was yesterday, when I received my Suburban water heater anode from Amazon, to replace in my truck campers Suburban water heater for the first time. I have however replaced them before on two travel trailers I have owned, so the process was not new to mer. I was surprised to find that although the packing on the new indicted Suburban, the threads would not engage. I verified the threads on the rod and the water heater were not stripped and used a small wire brush on the water heater to remove residual Teflon tape and any grit and still the rod would not thread. Took a closer and comparison look at both the old and new rods and discovered the new one has a course thread pattern, while the old, which went back in easily, has a finer thread. I went to a local RV dealer's parts counter today and picked up another, same thread pattern and it went in no problem.