There are 2 types of the inside structure of the screw-in insulator: the straight support core or the continuous support core, please see the below picture:

For screw-in insulator with straight support core, this structure is simple, the butterfly design can make sure the ring insulator being screwed into the wood tightly, this type is also higher cost performance.

For screw-in insulator with continuous support, this structure is more durable and  make sure the ring insulator being screwed into the wood more tightly, but the semicircle metal is easily exposed, so the production loss for this type is high, and of course, the price is high too.

We can make the screw-in insulator in different structure, welcome your enquiry!