what is GST rate on custom milling of wheat

SAC CODE 9988 has many services under 18% and some specified services at Nil, 5% and 12%...

For your clarification following services are at 5% rate...

9988	Manufacturing services on physical inputs (goods) owned by others, other than a) Services by way of job work in relation to- (a) Printing of newspapers; (b) Textiles and textile products falling under Chapter 50 to 63 in the First Schedule to the Customs Tariff Act, 1975 (51of 1975) (c) Cut and polished diamonds; precious and semi-precious stones; or plain and studded jewellery of gold and other precious metals, falling under Chapter of HSN; (d) Printing of books (including Braille books), journals and periodicals; (e) Processing of hides, skins and leather falling under Chapter 41 of HSN. b) Services by way of any treatment or process on goods belonging to another person, in relation to- (a) printing of newspapers; (b) printing of books (including Braille books), journals and periodicals.	5	28/06/2017
9988	Manufacture of handicraft goods. Explanation. - The expression “handicraft goods” shall have the same meaning as assigned to it in the notification No. 32/2017 -Central Tax, dated the 15th September, 2017 published in the Gazette of India, Extraordinary, Part II, Section 3, Sub-section (i), vide number G.S.R. 1158 (E), dated the 15th September, 2017 as amended from time to time.’.	5	14/11/2017
9988	(ea) manufacture of leather goods or foot wear falling under Chapter 42 or 64 in the First Schedule to the Customs Tariff Act, 1975 (51of 1975) respectively;	5	25/01/2018
9988	(iii) Tailoring services.	5	25/01/2018

Other then these, in general, service rate is 18% only.