The Japanese Standards Association (2000) and the International Organization for Standardization (2011) have standardized tactile bars (bar-shaped symbol on a stop key) and dots (dot-shaped symbol on a start key) that enable people with visual impairment to discriminate the keys on consumer products. However, to the best of our knowledge, there have been no studies regarding their recommended sizes and shapes in view of the establishment and modification of standards related to tactile bars and dots. The purpose of this study is to evaluate the influence of the sizes of tactile dots and bars on their discriminability to determine the appropriate size of tactile bars (as distinguished from tactile dots) regardless of the aging and tactile experiences, which markedly affect tactile acuity on the fingertips. Younger and older participants with or without visual impairment tactually discriminated tactile dots and bars presented individually, in random order, via a two-alternative forced-choice task. The results showed that participants discriminated tactile bars from tactile dots faster and more accurately as the dimensional difference between the bar length and width increased. In particular, younger sighted, younger, and older blind participants distinguished tactile bars of more than +2.0 [mm] length from tactile dots correctly. However, the older sighted participants required a bar length of +3.0 [mm] for accurate discrimination of tactile bars. In addition, younger and older sighted persons discriminated tactile bars with a length of +4.0 [mm] in less time, whereas younger and older blind participants were able to discriminate tactile bars of more than +3.0 [mm] length. On the other hand, tactile dots with a larger edge radius of curvature have higher discriminability than tactile dots with a smaller edge radius of curvature for dots of identical height.