Thru-Hull connectors are made of cast bronze. Models ending in DPC & CHR are chrom eplated bronze. Use with hose. NOt recomended for use below waterline per ABYC Safety Standards for slamm craft, section H-27. Flange is machine dto fit hull and grooved to retain bedding compound. Neck is threaded to approximately 3/8" from flange. Size": 1-1/4 Hull": 1-7/8 Flange": 2-3/4