Strong and versatile carbon nanotubes are finding new applications in improving conventional polymer-based fibers. Nanotube-reinforced composites could ultimately provide the foundation for a new class of strong and lightweight fibers with properties such as electrical and thermal conductivity unavailable in current fibers. A recent research has discovered that the best type of nanotube for polymer composite reinforcement is the small diameter multiwalled nanotubes (MWNTs). Here, a catalytic technique has been developed to produce narrow diameter bulk multiwalled carbon nanotubes of less than 38 nm. Structural characterizations including scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), thermo gravimetric analysis (TGA) and Raman spectroscopy conducted on CNTs grown on three different catalysts, namely iron, cobalt and nickel have indicated that the catalyst used affects their sizes and crystallinity. Results showed that the smallest CNTs could be obtained by catalytic growth on Ni catalyst. The study has proven that with the skillful use of catalyst, a range of narrow sized nanotubes could be produced, providing the material needed to investigate the optimum diameter for the best mechanical reinforcement of polymer composites.