ACH number: ACH stands for Automated Clearing House.
Usage: This number is used for electronic transfers, such as direct deposits, automated payments and other types of electronic transactions within the United States. Characteristics: ACH numbers are used specifically for transactions that go through the ACH network, which is a system for processing large-scale payments.

ABA number: ABA stands for American Bankers Association.
Usage: Also called a routing number, this number is used for both paper cheques and electronic transactions, including ACH and wire transactions.
Features: An ABA number identifies a specific bank in the US and usually consists of 9 digits. In many cases, the ACH number and the ABA number are the same, but some banks use different numbers for ACH transactions and traditional wire transactions. It is important to use the correct numbers depending on the type of transaction you are conducting.