New old stock upper gear case, Honda part number 215A1-960-772.  This part fits the following Honda Lawn Mowers.

HR21 SDA - HR21 1000001-1051093

HR21 SXA - HR21 1000001-1051093 

HR21-5 SDA - HR21-5 1019070-9999999 

HR21-5 SDAM - HR21-5 1019070-9999999 

HR21K1 SDA - HR21K1 1100004-1127597 

HR21K1 SXA - HR21K1 1100004-1127597