Comparative trials were undertaken using 16 types of guide-tubes of different caliber and external diamter: small caliber (1.35mm) and large cliber (1.80mm) tubes of eight types of external diameter (i. e, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5 and 6.0mm). 540 tappings was performed with a hard needle (length: 58.0mm, diameter: 0.16mm, head diameter: 1.25mm). The result can be summarized as follows: 1. Among the six small guide-tubes with 2.5-5.0mm external diameter, the larger external diameter was, the less sticking pain was experienced. 2. The four small caliber guide-tubes with 4.5-6.0mm external diameter caused significantly less sticking pain compared with the four small caliber guide-tubes of 2.5-4.0mm and the four large guide-tubes of 4.5-6.0mm.