Meaning of Block size in tcode R3AC1
The row number of internal table EQUI = block size set in R3AC1
For example if you have 110 equipment to be downloaded from ERP, there would be 3 inbound queues generated in CRM, the first two will each import 150 equipment and the left 3rd queue imports the left 10 equipment.
The transaction handling of each queue is isolated from each other, for example if there is some corrupted data on a given equipment in the 1st queue, the creation / update on the 1st queue ( 150 equipment ) will fail, however the left 150 equipment will still be successfully imported to CRM.
In tcode R3AC1 you can maintain block size for an adapter object.