The #12B A1 attachments will fit any British Standard 12B roller chain. The A1 attachment has 1 bent tab with a single hole.
12B A1 Attachment Connecting Link Dimensions
Pin Diameter (d2):5.72mm
Link Plate Thickness (T):1.85mm
Tab Width (G):16mm
Attachment Width (W):26.20mm
Width To Center Hole (F):19.05mm
Attachment Hole Diameter (d4):6.4mm
Attachment Height (h4):13.46mm
Connecting Link Clip Type:Spring Clip
Connecting Link Installation Tips
Spring Clip Connecting Links: The spring clip should be installed where the opening is facing away from the direction of travel. This will help prevent the spring clips from coming off. Like shown in the diagram to the right. Careful not spread the clip opening too far apart. This can make the clip more prone to falling off.
Cotter Pin Connecting Links: Cotter Pin Connecting Links The cotter pins pin legs should be spread about 60° apart. Like shown in the diagram to the left. Never reuse cotter pins that have been taken off. Never use commercial cotter pins as these are usually not hardened.