Comfortable retainer with tight fit around the watch strap: It retains the strap very well. 
Multiple sizes, 18mm, 20mm, 22mm and 26mm. With our without BBL logo! (Except 18mm, only blank atm)

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