While a couple of models actually preceded the model 17 (the Austrian army version was named the P80), the first model most of us associate with Glock is the model 17. The first guns imported into the US came with the AF serial number prefix and these early versions came with a thinner barrel in comparison to later models. In the collector circles, these are referred to as “Pencil Barrels” and have attracted quite a following.
Picture 1 below shows a side by side comparison and, though subtle, you will note the thinner profile of the barrel side walls next to a later 1st gen gun.
According to the Glock factory reps, there were approximately 25,000 1st generation model 17s imported to the US. Examples have been found with most serial prefixes between AA and EE. The pencil barrel was standard up until somewhere in the AM prefix serial bank with most of these guns staying in Europe.
Over the last several years interest in Glocks as collectible firearms has skyrocketed and with it the demand for these early variants. A run of the mill pencil barrel will routinely bring more than $2,000 at auction with high grade complete models bringing as much as $7,000.