A good quality gents adjustable expanding bracelet available in 4 patterns
Spring loaded end-pieces ensure fitting from 16mm to 20mm
Stainless steel back safe on most skins
Adjustable length by the easy removal or addition of individual links
 
The unexpanded length of this strap is about 15.0cms but can be expanded to about 24cms.
However stretching more than 18cms or 19cms is considered uncomfortable by most people.
The length of the bracelet can be easily adjusted by the addition or removal of individual links.

Extra links can be supplied and fitted at £0.30 each. 
Each link will add just under 4mm to the length
Don't forget to take your watch case size in to account in any length calculations.