Cassette Arms

What Riderman lacked in technological strength of V3, as well as the Riders before him (Rider 1 and 2), he made up for in persistence, smarts, and his wide array of prosthetic weapons that he had named the Cassette Arms (カセットアーム) to meet his needs. His weapons were also the basis for the "Rider Slash" and "Rider Shooting" finishing attacks.

The equipment of a bionic arm was a necessity for Joji Yuki, whose right arm was destroyed after being dipped into a pool of acid during an execution attempt, having been framed by Marshal Armor. However, Yuki was rescued by his fellow Destron Scientists who performed the operation which not only replaced his arm but allowed him to transform into Riderman to get his revenge.

Cassette Arms

 * Rope Arm (ロープアーム): Riderman's default/primary Cassette Arm, which is used in various ways: as a means of escape, climbing, and in combat. The arm itself has modified attachments for Yuki to use and adjust to various situations.
 * Hook Arm (フック－アーム): A hook attachment for climbing and combat.
 * Swing Arm (スウィングアーム): A mace attachment, which can be extended and used as a flailing weapon.
 * Net Arm (ネットアーム): An attachment where Yuki's arm can shoot out a net to capture and restrain enemies (by Kamen Rider Spirits, it appears that this net is fireproof).
 * Sickle Arm: An unused attachment, which has been seen in various promotion; and yet, wasn't used in the series. Based on the photos, it is assumed it is simply used for combat.
 * Power Arm (パワーアーム): Riderman's strongest weapon, which increases Yuki's attack in battle. Its primary use is to hack away at both obstacles, such as doors, and opponents. This weapon could've been easily used as a finishing attack, according to some fans. This weapon is the first instance of a Rider using a blade against a monster, which would later be a frequent armament in the Heisei Era-Riders.
 * Drill Arm (ドリルアーム): Another weapon could've been easily used as a finishing move. It was only seen being used as an infiltration tool. It must be plugged in order for it to work best, although it will still work otherwise (by Kamen Rider Spirits, it appears to work just fine without external power).
 * Machine Gun Arm (マシンガンアーム): A concept drawing seen in Ishinomori's artwork, this Cassette Arm would not be used in Kamen Rider V3 and resembles a Gatling gun. A revised version of this weapon was seen in the Kamen Rider Spirits manga. It was used to destroy the revived Marshal Yoroi in the manga and had the appearance of an assault rifle machine gun. However, this weapon eventually made a live action appearance in the film Kamen Rider Taisen. Riderman uses it to block Kamen Rider Fourze's Gatling shoot attack. It appearance here resembles his other Cassette Arms with a machine gun muzzle attached to it. This weapon is the first instance of a Rider using a gun against a monster, which would later be a frequent armament in the Heisei Era-Riders.
 * Spray Arm (スプレーアーム): Currently, it is only an unused concept. Its function was described as a weapon which sprays gas or smoke to distract adversaries.
 * Octopus Arm (オクトパスアーム): Currently, it is only an unused concept. Its function is described as a climbing tool, each finger on the hand resembling octopus tentacles.

A.R. World
The A.R. version of Joji Yuki from the World of Decade, while not shown transforming into Riderman, had a prosthetic arm similar to the original. He had lost his right arm in similar circumstances under the orders of the Great Leader of Dai-Shocker having previously served Dai-Shocker as a scientist.
 * Blaster/Cannon Arm (ブラスター/キャノンアーム): This weapon is used while he is in human form. It is activated when Joji rips off his prosthetic arm revealing a high powered beam cannon. This is seen in Kamen Rider Decade: All Riders vs. Dai-Shocker and in "The Next Decade" MV.

SD
In the OVA Kamen Rider SD: Strange!? Kumo Otoko, the SD Riderman has the Power-Arm equipped through the whole movie, although it seems to function like the rope arm too as demonstrated in the opening.