Best-selling 3D printer parts and spares of 2021

How this ranking is built

Amazon publishes a sales rank for every product, updated continuously. Rank 1 in a category is its best seller. We take each product’s full rank history and compute a duration-weighted median for the calendar year: the position it actually held for most of that year, rather than an average, which a single viral week would distort.

“Best rank” is the highest position it reached at any point — useful context, but a product can spike to #200 for a weekend and spend the rest of the year at #4,000, which is why the ranking uses the median.

Two things this page cannot tell you

Sales rank is not units sold. Amazon does not publish sales figures. Rank is a good relative signal — something at #500 is genuinely outselling something at #5,000 — but the gap between two adjacent entries here could be large or tiny, and there is no honest way for us to say which.

Older years are biased towards survivors. The products we hold history for are the ones selling today. One that sold well in 2021 and was discontinued is not in our catalogue, so it cannot appear in that year’s list even though it belongs there. The further back you go, the more that matters — which is why we show how many products each year was ranked from, and refuse to publish a top ten when that number is too small.

Why not rank by reviews?

Review counts favour products that have been on sale longest, and star ratings on Amazon cluster so tightly between 4.1 and 4.6 that they separate almost nothing. Sales rank at least measures what people actually bought. We show the rating alongside because it is useful, not because it decides the order.