Abstract: In a conversion sleeve comprising a large diameter part, a small diameter part, and a tapered diameter part interconnecting said two parts, a ferrule insertion stop part is formed on an inner circumferential surface of the tapered diameter part and/or inner circumferential surfaces of the large diameter part and the small diameter part adjacent to the tapered diameter part. An optical adapter comprises a split sleeve having a slit formed therein throughout the entire length in the longitudinal direction thereof, particularly a conversion sleeve, and an adapter housing having a sleeve retaining part in which the sleeve is inserted and retained. The sleeve retaining part is provided with an engagement part comprising a recessed portion or/and a projected portion. The split sleeve is provided with a counter engagement part comprising a projected portion or/and a recessed portion which engages with the recessed portion or/and the projected portion of the engagement part.

Abstract: In a conversion sleeve comprising a large diameter part, a small diameter part, and a tapered diameter part interconnecting said two parts, a ferrule insertion stop part is formed on an inner circumferential surface of the tapered diameter part and/or inner circumferential surfaces of the large diameter part and the small diameter part adjacent to the tapered diameter part. An optical adapter comprises a split sleeve having a slit formed therein throughout the entire length in the longitudinal direction thereof, particularly a conversion sleeve, and an adapter housing having a sleeve retaining part in which the sleeve is inserted and retained. The sleeve retaining part is provided with an engagement part comprising a recessed portion or/and a projected portion. The split sleeve is provided with a counter engagement part comprising a projected portion or/and a recessed portion which engages with the recessed portion or/and the projected portion of the engagement part.