Comfortable retainer with tight fit around the watch strap: It retains the strap very well. 
Multiple sizes, 20mm, 22mm and 26mm. With our without BBL logo! 

What differs mine from others on this website is there is a slight roundness to this for more comfort, 

My watch strap retainer / loop broke so I did a quick design and printed myself a new one instead of buying. 
 

.f3d is provided as a download