HSN CODE

GST rate 18%...... You can choose either of the following.....

1.   998349 .....  Other technical and scientific services n.e.c.

2.  998714 .....  Maintenance and repair services of transport machinery and equipment

When you supply tipper as a whole (billed with material) it will not be just service......

It will fall under HSN code '8707' with 28% GST

As you are not trader of material and as such it will be considered as cost of tipper......

hence attract 28% GST.

Another option is to consider it as repairs with material, under composite supply, where the rate as a whole, will be applicable as per that applicable to the essential part fitted in the body.

Rate will be the rate as applicable to main part which is fitted or fabricated by you. (may be 18% or 28% depends)

HSN code under '998714'