* Series 0: Wire-keyguard design. Unknown serial number range, but fairly early. 
                    * Series I: from about 10xxx to 20xxx: 
                      In my opinion, the nicest model. An elaborately engraved horn with 
                      funky offset side chromatic Bb/C and altissimo E vent keys, a microtuner 
                      neck and rolled tone holes.
                    Oddly, the 
					Toneking model lacks the offset side keys and additional pearl keytouches of the New King model. I don't have enough data to determine if the bore is any different. Maybe, but, considering that these horns were made in such low quantities, it's more probable that it's not. 
                    * Series II: beveled tone holes and 
                      left-hand bell keys  were used on about 500 to 1000 
                      horns after Keilwerth moved from Czechoslovakia to 
                      Germany. These horns are such a radical departure from the Series 
                      I, they could be considered a completely different model. I believe 
                      this is intentional, as Amati co-opted the Toneking name and design 
                      (see below). There may also not have been any Tonekings of this series.
                    This model may have been developed in conjunction with Kohlert, as some rumors suggest. 
                    The other interesting thing about these horns is that 
                      they're one of the four I'm aware of that had beveled tone holes. 
                      The others are early 
                        Couesnons, Martin and some early Bueschers.
					There are also 
					at least two generations of these horns: bell keys on the 
					left or bell keys on the right.  They otherwise look 
					identical.
                    * Series III: from about 21xxx to 45xxx: 
                      The introduction of the horns with the stunning lucite keyguard -- 
                      but the elimination of the microtuner neck. Rolled tone holes seem 
                      to be added randomly to these models.
                    I've been asked about the horns that have METAL keyguards in the same shape as the lucite ones: are they original? My answer: possibly. 
                    I can imagine, because the lucite keyguards are so brittle, that after a year or two, Keilwerth offered the metal guard as an option -- or they used them as warranty replacements. However, I've been unable to find a serial number range for "just metal" or "just lucite", so the idea that the metal keyguards are replacements, either from the factory or other 3rd party company, is probably the most accurate. 
                    
					* Series IIIa: In 1956, an interesting horn shows up: the
					 V. Kohlert & Sons model 
					with a label on the back, that reads, "JGK: The Best in the World" and "Made in Czechoslovakia". It's an odd horn because it doesn't look like any other New King model. The reason for this is because I don't really believe it's a Keilwerth, but an Amati horn. Take a look at the below article regarding the Amati Toneking and my notes on the
					 Kohlert page.
					 
                    * Series IV: from about 45xxx to 905xx. 
                      These are a somewhat cheaper looking horn, with sheet-metal keyguards.  
					This is the series that the extremely famous
					H-Couf, 
					Conn DJH Modified, King Tempo, Armstrong Heritage, 
					Bundy/Bundy Special (and a few others) are stenciled from.
                    I can confirm that the Keilwerth-made Bundys are great 
                      horns, but remember that they were marketed as 
                      student horns  and may 
                      be made from lower quality materials and may lack in some features (see, 
					for instance, this 
                        link, which compares a Series I to an Esquire model tenor). 
                  
                  This instrument is one of only 
				two made and is in excellent original condition. Here's the 
				story!! This sax came out of the Keilworth [sic] factory a few 
				years ago. The factory had two graduating apprentices, and for 
				their final project were given the task of making a Low A bass 
				each. The sax has no markings at all and no sn# as it is a 
				handmade prototype, (You can tell its handmade as can see where 
				they have moved a few posts etc (trial/error) for the keywork.) 
				A major dealer in Europe bought them both from the factory, sold 
				one to Switzerland and here's the other!!!!