Faber Castell made the first pencil of this kind in the world (lead holder/clutch pencil). This one is the most improved version of the successful TK9400, which simply added the sharpener and the clip! I have almost all the pencils of this kind from all companies, the TK4600 is by far the most reliable of all and by a long shot. Simply, the best pencil in the world for freehand or technical drawing. Whether this one or its previous versions (same pencil, just designed for different situations) are the best out there. Don't be fooled by its low price, or if you see others made of metal, etc., this one is the best. The TK 9400 that started it all comes in various versions and is also made for Freehand or Technical drawing. The TK 9500 is designed for situations like school/colleges, while this TK4600 is made to take with you everywhere, which is why they added the sharpener to the button! Hence the clip, which is removable, so easily by twisting it and pushing upwards, you can remove it to make the pencil even more comfortable, making the TK4600 automatically the most versatile! You can use any brand of leads you want, as long as they are 2mm thick. (The best for drawing are from Faber Castell-TK 9071) If you want hardness, from 4B to 6B, then you need to buy the Faber Castell TK 9400 3.15mm, which is almost the same pencil, a bit thicker, with a more comfortable grip (when held in writing position), designed for softer graphite 4B and 6B. A smart idea that only this company does. The others only produce them in 2mm thickness and besides the leads breaking easily, their graphite quality is not good either. So, I would recommend leads only from Faber Castell, as here in Greece, they are by far the best you will find. Only the leads from UNI Mitsubishi are worth it, but you can only buy them online from foreign stores.
;Extra guide for the best mechanical pencils for every use: My favorite mechanical (0.3mm - 0.9mm) and the best for drawing are the Pentel Graphgear 500 0.5mm and as a slightly cheaper option, the legendary Pentel P205 0.5 mm. For writing and carrying with you every day, if you want 2mm leads, the best pencil for sketching, and at the same time, the most versatile pencil of all time, is the Koh-I-Noor 5340 (5.6mm). What can one say about this pencil! Just the options in leads, and the fact that the same company produces the best Red Chalk (Sanguine) and Sepia, is enough! Just try it, those of you who are into sketching, and you will discover it; it is a fact after all and not just my personal opinion. If you want a mechanical pencil in 0.5mm/0.7mm, that you can carry with you for writing/notes, etc., then the best is the Pentel Kerry with Pentel Ain Stein 2B leads, either in 0.7mm or 0.5mm, depending on your preferences!
P.S. These are, by general consensus, the best mechanical pencils in the world and not just my personal opinion and experience. Having tried almost everything at a professional level, I have confirmed that mechanical pencils are one of the rare cases where the saying "you get what you pay for" does NOT apply absolutely. This is confirmed, as the best for drawing are almost always not the most expensive, but the pencils in the mid-price range. (TK9400-TK4600 and Pentel Graphgear 500 0.5mm or Pilot S10 0.5mm for linework, are the best pencils for drawing)
P.S. 2 The internal mechanical parts of the TK 4600 and the tube that contains the tip are all made of brass. The spring, the button/sharpener, and the grip are made of steel. Even the Rotring, inside has a lot of plastic in mechanical parts, tube, etc., this one does not, it is all A quality metals.