Business / Finance / Gnomes: Mortgage-backed securities (M.B.S.) on which registered holders receive an aggregate principal and interest payment from a central paying agent on all their certificates. Principal and interest payments are disbursed on the 20th day of the month. GNMA-II M.B.S. are backed by multiple-issuer pools or custom pools (one issuer but different interest rates that may vary within one percentage point). Multiple-issuer pools are known as 'jumbos.' Jumbo pools are generally longer and offer certain mortgages that are more geographically diverse than single-issuer pools. Jumbo pool mortgage interest rates may vary within one percentage point.