An employee of Japan's gadget maker Thanko holds the silicone-based thumb extender at its store in Akihabara shopping district in Tokyo on September 25, 2014

Human thumbs are just too stumpy to navigate bigger-than-ever smartphone screens, but a Japanese gadget maker has a solution: a thumb extender.

Enter Japan-based Thanko that is hawking a silicone-based device called the "Yubi Nobiiru", or "stretched finger", for 1,480 yen ($13.55) apiece.

The thumb extension lets users master large-screen devices such as the iPhone 6 Plus and Samsung's oversized Galaxy Note with just one hand.

The fake digit slips over user's real thumb to produce a life-like appendage boasting an extra 15 millimetres (0.6 inch) of length.

That means users can reach any spot on the bigger iPhone's 5.5 inch screen, perfect for urban commuters clutching a briefcase or a subway strap on packed trains.

A conductor at the hollow gadget's tip ensures the screen registers its touch.

"Do you think new smartphones are too big and it's difficult to touch the far corners of the display?" Thanko says on its website.

"Wear this stylus that looks exactly like your thumb, only longer!"

A Thanko spokesman told AFP that the firm wanted to make something unique to the pen-shaped stylus models already on the market.

"We've seen steady Internet sales and some customers abroad are buying it," he said of the extender, which went on sale in May.

This week, Apple said it broke its sales record for the opening weekend of a new iPhone model, delivering 10 million in the first three days and boasting it could have sold more if it had them.

An employee of Japan's gadget maker Thanko holds the silicone-based thumb extender at its store in Akihabara shopping district in Tokyo on September 25, 2014