Adafruit Half sized breadboard is a suitable breadboard for prototyping small to medium projects. Its dimensions are 5.5cm x 8,5cm with a standard double-strip in the middle and two power rails on both sides. You can pull the power rails off easily to make the breadboard as thin as 3.5cm. You can also "snap" these breadboards together either way to make longer and/or wider prototyping area.
Adafruit Half sized breadboard - General Specifications
Half size breadboard
Suitable for small projects
Standard double-strip in the middle
Two removable power rails
Can be snapped with other breadboards to make a longer or wider prototyping area