Oh I adore this. At first sight, I wondered if this was a vintage piece as it has mid century retro vibes, but according to the registration mark inside, it dates to 1849, which only makes me love it more. 
 
Those bold ridges, and the fine detailed edging, this is a definite statement. 
 
A hinged fitting, with a well functioning box clasp, which closes with a definite click, and further backed up with a safety chain. 
 
Be warned, this is for a smaller wrist - the only reason it isn't staying with me! 
 
Tested as 15ct gold
Design registration mark for February 1849. 
Weight approx 30.63g
Width approx 21mm
Inside circumference when closed approx 6 1/4 inches, suited for a wrist of 6 inches or less. 
Some small dent to the peaks of the ridges, as shown in photos. One section has been historically replaced, with a slightly lower, wider profile.