Among the many remarkable properties of single-walled carbon nanotubes, it is their mechanical and electronic properties that stand out [1]. The excellent resistance of carbon nanotubes to bending [2 –7] should lead to future applications of the tubes as a high-strength, lightweight material. Turning to their electronic properties, we find that, at ambient temperatures, single-walled carbon nanotubes may be either metallic or semiconducting, depending upon their helicity [8– 12]. It has been shown [13] that tubes with different helicities may be joined together with one or more pentagon-heptagon (5-7) defects to form different electronic heterojunctions, thereby opening up the intriguing possibility of forming all-carbon based microelectronic devices [14,15]. Some of these remarkable theoretical predictions have recently been confirmed by scanning tunneling microscopy (STM) experiments [16]. However, if the dream of producing an all-carbon-based microelectronics is ever to be realized, then different methods will be needed to produce a variety of devices. Here, we present the results of a large-scale study of the mechanical transformations of strained nanotubes in the presence of ad-dimers and show that this combination may well turn out to be a natural route for the formation of all-carbon nanotube-based quantum dots. Ad-dimers are likely to be present in small amounts on as-grown carbon nanotubes, or they may be deposited there with a STM tip or other methods. The formation of quantum dots with ad-dimers is particularly favorable for the n ,0 zigzag tubes. Specifically, we show that ad-dimers induce plastic behavior on tubes that are otherwise brittle. Before discussing the simulations, we briefly review the