postgres=#
postgres=# CREATE TABLE test (a BIT(3), b BIT VARYING(5));
CREATE TABLE
postgres=#
postgres=# INSERT INTO test VALUES (B'101', B'00');
INSERT 0 1
postgres=# INSERT INTO test VALUES (B'10', B'101');
ERROR: bit string length 2 does not match type bit(3)
postgres=# INSERT INTO test VALUES (B'10'::bit(3), B'101');
INSERT 0 1
postgres=# SELECT * FROM test;
a | b
-----+-----
101 | 00
100 | 101
(2 rows)
postgres=#
postgres=#
postgres=# drop table test;
DROP TABLE
postgres=#