Flat Mineral Watch Glass. (there might be ±0.2mm difference). 25/25.5/26/26.5/27/27.5/28/28.5/29/29.5/30/30.5/31/31.5/32/32.5/33/33.5/34/ 34.5/35/35.5/36/36.5/37/37.5/38/38.5/39/39.5/40/40.5/41/41.5/42/42.5/43/43.5/44/44.5/45/45.5/46/46.5/47/47.5/48/48.5/49/49.5/50mm.