This type of uke system is adjustable so it can be used with most uke sizes and is designed so that no strap buttons are needed.
UK-25 Blue, Grey & Black Woven Cotton Adjustable Ukulele Strap
• Blue, Grey & Black jacquard woven top welt
• High quality nylon web backing
• Genuine leather end caps
• Fits most ukes & classical guitars
• 1 1/4” wide
• Adjustable in length from 27”-37″
Ukes almost never come with strap buttons or any other good way to attach a strap. This around the neck strap style is the most popular way to deal with that problem. This is the same method that classical guitar players use and because they have a wide range of adjustment for length, the Walker & Williams UK series straps can also be used for many classical guitars.