Check the listing for details. Ronstan Series 50 All Purpose Block - Double. Condition: New. Listed at 71.27 USD. Series 50 All Purpose Block - Double Features: Exceptionally high working loads Low maintenance, long service life Self-lubricating Acetal polymer sheave ensures low friction and extreme durability Slotted pin shackle eliminates fouled lines Lockable swivelling head post All purpose (AP) blocks are a great all around solution. Self-lubricating Acetal polymer sheaves running on polished stainless steel races perform equally well with dynamic loads and high static loads. For durability and a long service life, these blocks are the right choice for sheets, halyards and control line applications for cruising and racing.Head can be locked at 0° or 90° by engaging the grub screw in either the 0 or 90 degree position. Applications: Mainsheet and halyard applications, vang and spinnaker control lines on boats to 10m (33ft) S60 - on boats up to 12m (40ft) Materials: Grade 316 stainless steel load strap Impact and UV resistant, fiber reinforced Nylon cheeks