Spring bar
Leather, NATO, rubber, most straps
A sprung tube between the lugs. Compress one tip with a forked spring bar tool, lift the strap clear, then seat the new bar tip first into the far lug hole and let the near tip snap home. No links, no pins, no force into the case.
Collared pin
Seiko and most steel bracelets
A split sleeve grips the pin by friction. The joint releases in one direction only, marked by a stamped arrow on the underside near the clasp. Pushing against the arrow jams the collar harder. Read the arrow, support the link, push the pin straight through.
Screw link
Rolex, Omega, Tag Heuer, Tudor
A real machine screw, often with thread lock. It needs a correctly sized watchmaker screwdriver, never a pin pusher. Wrong size cams the slot and the link is then scrap. Counter-hold the head, break the lock with steady pressure, unscrew fully before pulling the link.
Pin and ferrule
Casio, Citizen, many quartz bracelets
A straight friction pin held by two tiny tubes, the ferrules, one in each neighbouring link. The ferrules fall out when the pin leaves, so work over a tray. Push straight, keep every ferrule, refit the pin from the same side it came out.
Apple Watch
Button and slide, all models
No spring bars, no links, no pins. Press and hold the band release button on the case back, slide the band sideways out of its channel, slide the new one in until it clicks. If a band will not fit it is the wrong case-size group, not a tool problem. Any watch tool is irrelevant here.
Buckle and loop
Leather and fabric straps
Adjusted at the buckle, not the case. If no hole sits right, a leather punch adds one in line with the rest. The strap should sit on the second or third hole when new, so there is room to move in both directions as it wears in.
Quick reference
Which mechanism do I have?
Turn the bracelet over and look at the removable links near the clasp. A flush round head with no slot is a friction or collared pin. A visible screw slot is a screw link. Stamped arrows mean a directional collared pin. A round button on the case back with a side channel is the Apple Watch system. Holes and a buckle mean a strap, no pins involved.
How many links do I remove?
Put the watch on, pinch the slack, count the excess links. Split the count across both sides of the clasp so the clasp stays centred on your wrist. Use the half link by the clasp for an odd number. Remove one link at a time and re-check the fit before going further.
Which tool for which mechanism?
Strap change needs a forked spring bar tool. Friction and collared pins need a pin pusher plus a holder block and tweezers. Screw links need a correctly sized watchmaker screwdriver and nothing else. The Apple Watch needs no tool at all. Buying the wrong tool causes most of the damage we see.
My pin will not move.
On a collared bracelet the pin only exits in the direction of the stamped arrow. Pushing against it jams the collar harder. Reverse the link, follow the arrow, support the link in a holder so the force runs through the pin and not the joint. On a screw link, stop: it is a screw, not a pin, and forcing it ruins the slot.
My new Apple Watch band will not fit.
It is the wrong case-size group. The smaller cases share one band size and the larger cases another. Match the band to the case size, not to a tool. There is no on-watch adjustment and no tool involved at any point.
Should I just go to a jeweller?
If the mechanism is a screw link with thread lock and you do not own the exact driver, yes. The job is twenty minutes and inexpensive, and a camed screw costs far more than the service. For spring bars and friction pins the right tool pays for itself on the first band.
By brand
Not sure which system you have? Start with the main guide. It walks every mechanism and the four mistakes that cause almost every avoidable scratch.