They are the same NEB 5-alpha cells just provided in different transformation efficiency and different formats. C2987H is NEB 5-alpha competent E.coli with a high efficiency of 1-3X10E9 cfu/μg pUC19 DNA. C2988J is NEB 5-alpha competent E.coli with a subcloning efficiency of >1X10E6 cfu/μg pUC19 DNA. C2987H is packaged with 20 single-use transformation tubes containing 50 μl of competent cells each. Plasmid or ligation product can be added directly into the transformation tubes for convenience. C2988J is packaged with 6 tubes containing 400 μl of competent cells each. The tubes must be thawed on ice and 50 μl of cells should be pipetted into your own transformation tubes prior to transformation. Each tube contains enough cells for 8 transformations with the benefit of reducing the cost of each transformation. Refreezing the competent cells after thawing is not recommended since it will significantly reduce transformation efficiencies.