Not using Regex, and probably very expensive in a large dataset, but it works given the example strings in your question.
DECLARE @strings TABLE (string VARCHAR(100));
INSERT INTO @strings
VALUES ('CINTA NYLON CT708 DE 120MM X 1000MTRS'),
('CINTA NYLON 102MM X 1000MTRS');
SELECT string,
REVERSE(LEFT(REVERSE(SUBSTRING(string, 0, CHARINDEX('MM', string))), CHARINDEX(' ', REVERSE(SUBSTRING(string, 0, CHARINDEX('MM', string)))))) AS mm,
REVERSE(LEFT(REVERSE(SUBSTRING(string, 0, CHARINDEX('MTRS', string))), CHARINDEX(' ', REVERSE(SUBSTRING(string, 0, CHARINDEX('MTRS', string)))))) AS mtrs
FROM @strings;
"CINTA NYLON CT708 DE 120MM X 1000MTRS".match(/(\d*MM)|(\d*MTRS)/gi)