Quality one piece Pivotal fitment seatpost from Stay Strong, available in 3 sizes. 

22.2mm sizing for old school or mini/junior sized seat tubes. 250mm length. This size allows you to run modern Pivotal seats on most old school bikes. 

27.2mm for some alloy framed race bikes and dirt jump bikes. 250mm long. 

31.6mm for some larger diameter alloy frames and MTB. 320mm long. 

Pivotal fitment for pivotal seats only. Not compatible with railed or tripod systems