I have bought these caps several times for different projects I have done. They fit perfectly in a 1" square welded pipe and appear to be made of very strong plastic.
π 50 Pack of P MAP Maple Pocket Plugs
7 Review
WIDGETCO White Hole Plugs
9 Review
π§Ό Efficient Cleaning with Canplas 193064 Flush Cleanout - 4 Inch Diameter
π Marinco 6365CRN Locking Plug 250V: Secure and Reliable Power Connection Solution
π§ Inch Stainless Steel Brackets - Includes 80 Brackets
8 Review
π© Enhanced Durability and Stability: Outside Joining Aluminum Profile Bracket
Stainless Steel π© Fastener Hardware by BIGTEDDY
π© N100 792 National Hardware Plated Holder