シームレス is a loanword often used in technical or IT contexts, while 継ぎ目なし is the native Japanese equivalent used in everyday and physical contexts.
seamless steel pipe
Standard kanji spelling.
Variant with 継目 instead of 継ぎ目.
Variant using 無し instead of なし.
Rare combined variant.
Compound of 継ぎ目 (つぎめ, 'joint, seam') + なし ('without'). The spelling 継ぎ目なし is the most common representation.