substantially planar surface 54 of the needle bar housing and the surface 52 being adapted to abut a similar substantially planar side surface 56 of the holding block 48 thus the surfaces 50 56 are reference surfaces for providing acurate positioning of the holding blocks 46 48 in the vertical and in the front to rear directions when the holding blocks are mounted as hereinafter described the needles 22 24 are disposed vertically within bores in the respective blocks intermediate the respective side surfaces and secured by conventional securing means such as set screws 57 disposed through each needle block 46 48 is at least one bore 58 60 extending through the respective block in the direction transverse to the longitudinal direction of the needle bar and similar bores 62 extend through the downwardly depending leg of the needle bar housing 44 the bores 60 and 62 may be of substantially the same size the bore 60 being of a size for freely receiving the stem 64 of a bolt 66 the bore 58 which is smaller than the bore 60 is tapped for securely receiving the threaded end of the stem 64 when the bores 58 62 are in alignment whe so aligned the needles 22 and 24 are staggered as aforesaid however since the bore 60 is larger than the stem 64 the needle holding block 48 may be moved slightly relative to the block 46 to vary the stagger of the needles slightly relative to the on gauge stagger prior to securely tightening the bolts 66 into the needle block 46 at each.