For shrinkage protection from inside.

Variants
• WR3/8-60 – Pisco Insert Ring 3/8" x 0.24"
• WR3/8-70 – Pisco Insert Ring 3/8" x 0.28
• WR3/16-30 – Pisco Insert Ring 3/16" x 0.12"
• WR1/4-46 – Pisco Insert Ring 1/4" x 0.18"
• WR1/4-42 – Pisco Insert Ring 1/4" x 0.17"
• WR1/2-96 – Pisco Insert Ring 1/2" x 0.38"
• WR1/2-85 – Pisco Insert Ring 1/2" x 0.33"