Hello. I have a hard lump in the shaft skin
Could be Sebaceous Cyst or Calcified Plaque
Thanks for query You have not mentioned your age in your query .
.Based on the facts that you have developed a painless hard lump in shaft of the penis after masturbation .
This could be either a calcified plaque or a Sebaceous cyst ,However the diagnosis can be confirmed only on clinical examination by a qualified general Surgeon and doing Ultrasound Scanning of penis
Further treatment will depend upon result of this test and final diagnosis.
Hope I have answered your query ,please feel free to ask if you have more questions,I shall be happy to help you
Thanks and Regards.