YANMAR - Diaphragm B 

Part Number - 196420-02722

Fits To - SDe15(*), SDe10(*), SDe7(*), SDE10, SDE15, SDE7, SD20 SD20(*), SD20A-S, SD20B-S, SD20C-S,  SD31(*), SD30, SD25(*), SD40(*), SD40-4T(*), SD50-4T(*), SD50

You may wish to look at the following parts 

Inner Diaphragm Securing Band - 196420-02730

Secondary Diaphragm Outer Securing Band - 196420-02740

Sealing Diaphragm A - SD20,25,30,40,50 - 196420-02712

Outer Seal - Flexible Rubber Fairing -SDe7-15 SD15-25 - 196420-02551