Non SEL bracelet-SEL bracelet:
Solid end-links (the link that connects to the case and contains the spring bar) are often abbreviated as SEL and are normally a characteristic of more expensive watches. Most "Poor Man's" Watches feature hollow end links regardless whether the bracelet links are solid or folded. The links of a bracelet are normally connected by so called link pins. At the clasp and at the end-links you will find so called spring bars. They basically consist of a metallic tube, a spring in the middle and the two ends that match the holes in the clasp or the holes in the lugs of the watch case. Always be careful when removing spring bars. As the name suggests, they can fly away pretty easily.
This fact is simple to explain: a hollow end-link is quite easy to fit to a watch case. A solid end-link has to be manufactured with high precision to match the case exactly.
pmwf
Non-SEL